I have just ordered the No 90098.

Again you answer before I manage to formulate the question , which is great. Will look closely at the $30 ones and decide thanks.

It is confusing because the parts keep changing order as one looks at them but as far as I can make out the situation is as follows:
Parts  with No. 900 ending in 59,24,56,82,64,84 are sold out, that includes the one you recommended. Available are Parts with No 900 ending in 31,94,25/32/57,35,76  and two more expensive red ones 47 and 44/45.
So which of the available parts would be easiest to adapt?

Sorry, I posted the last comment without realising you had already answered. I will check again to veryfie it is sold out and get back to you.

It has 8254 written all over, it has a Bachmann China on the bottom and a little round sticker on each side July 1910 34942.
I am now a bit worried the link you gave me says SOLD OUT. If the right one is sold out can I perhaps adapt another one?

Thank you Bill,
I will most likely buy one today, but I want to make sure my locomotive is the one you say, how can I identity it?
Does the said part include the engine?  I've looked at the Bachmann page before and noticed there is a green one for $50 will it not fit?

Chuck, I've posted the events of a small catastrofe on my 4 0 6 thread.

Either I've gotten to the bottom of the problem or I've made it worse.
I first turned the loco upside down and held wires from the power supply to  the wheels but I soon got tired of holding them in place so I tied the wires to the front wheels,  everything seemed to work fine, no slowing down but I did notice a slight crunch when going forward, after a while the crunch became louder the loco slowed down , a little smoke , big crunch and stop. The last time I opened the bottom to fix the front wheels that nylon gear wheel did not look like that. So either the gear wheels were already worn and that was causing the problem or the motor was running against great resistance and the nylon got to hot and the teeth of the nylon wheel disintegrated.
I hope the two nylon gear parts are available, I now need instructions on how to take apart the necessary to be able to change the nylon parts. And to find out if something is causing friction where it should not.
PS. I intended to post photos of the state the nylon wheeĺ is in and the inside of the locomotive but I get an error message "file to big" even when I try one with such low resolution one can't see anything.

Kevin, The three Black  locomotives of the same scale (1:20.3). On the two photos. The larger one RioGrande, Are they all Bachmann?  What are the model names?

About the locomotives depicted in the Chart: 
In  the real locomotives part of the chart the 2 foot gauge as well as the 7/8 n2 scale on the  Model locomotives part of the chart look very unstable because the track looks very small for their size. I suppose both the real and the model must be rather prone to tip over?

K, thank you so much for the very thorough explanation on the size and history behind my Locomotives, and the photos and charts, really fascinating.

Chuck, I guess you're referring to my post on the 4 0 6 that stops. I'll try the power to individual pairs of wheels tomorrow, is the drivetrain the same part Bachmann calls the Loco chassis? They are indeed inexpensive right now. But before I buy one I'd like to be sure it isn't the wires or the motor or the power supply.

I suspect in this case there should be 16, they are the longer less bent rails. I'l check the diameter of the circle tomorrow. I also suspect the problem might be in the locomotive because I just tested the Olumana on this track and it runs like a clock, steady for ever. I don't' know how the 4 6 0 should run but it seems to lack power, perhaps something wrong with the wiring or the motor? It looks like its been tampered with a bit. The wires in the front where preventing the small front wheel part from moving and the back wheels were incorrectly placed when I got it.

The locomotives does not have the extra switch in the front, only one for smoke so I switched polarities on the power supply,  same thing good backwards , stops forward after a short while, I have bought everything second hand on ebay , no starter set, the rails are Aristocraft brass but used and not so clean, the ties have no screws , I have them but have not yet installed them , the power supply is LGB 50081, the circle has 14 rails, my two other locomotive work well on this track. I have no volt meter but I will borrow one on tuesday or Wednesday and will write.
Thank you again.

Thank you indeed,
I intend to run each loco with cars designed for it, the circus loco with its circus cars only, the Olumana with smallish gondolas, the Swannee River with Swannee river passenger cars, And I expect the  Spectrum loco with spectrum gondolas.
I intend to get Scot Laurence's Scale/Gauge Illustration, sound like something really worth having, thanks for the recommendation.
P.S.You seem to be a real Bachmann expert, I wonder if you can give me a solution to a problem  I posted on a message about the Swannee  River Special that stops running. It has been viewed over 30 times and no replies yet.

This is a coment on a topic called Car sizes? A  very informative  topic that has not been posted in for at least 120 days so I was advised to open a new topic.

I'm  just starting on G, my first ebay acquisition was a rather expensive LGB OLUMANA, the auction bids just rocketed towards the end.  I was so disappointed when it arrived to see it was so small, really tinny.  It is very beautiful, has a grand story  and runs great so I like it alot  even though it is so small for a G.  My second ebay win was an LGB Circus Loco it is bigger, what a relief! It is in perfect condition and very strong. My third ebay winning was a Bachmann big hauler,  Swannee River Special with tender, uncredibility cheap on ebay , I could not believe how big it is. It is troublesome and delicate but I'm enjoying fixing it and I love the size and looks. My latest is a Spectrum 38 ton Shay that has not been delivered yet,  I hope it's big. If the cars for it are the biggest I suppose it must be. Big is wat G is all about. Is it not?