Sorry to hear we're losing another one.
Daryl

Len, you are correct.  On30 did exist before Bachmann brought out the RTR trains but it was more a scratch build niech market  than a main stream product line.  Most of the people, including myself, saw this "new" scale and became interested because of space factors.  I can scoot by with 30" radius for my K's but in On3 I would have to go at least 38" to have a decent looking run.  Dept 56 did introduce the first set with Bachmann's engine and then Thomas Kincade sets and others hit the marketplace as well.  Of course these were all licensed Bachmann products.

I was in HOn3 for years before Blackstone and their amazing engines and dabbled in Sn3 for a few years but the expense was killing me.  I got really excited for On30 when I learned about MMI's engines that depicted Colorado narrow gauge road engines.  I bought a whole bunch of 0N30 years ago in New Yrk when ridge Road Station went out of business, including 1 MMI K engine way back in the early 2000's.  I found them about 4 years ago in the garage and the bug bit again.  Sold all of my garden railroad equipment and bought several cars and engines at a relatively good price. 

Hey RailMan,
Saw some of your posts and have some other solutions for you but I will post there.

The real difference between 0n30 and 0n3 is the width between the rails, but there are some subtle differences in sizing.
Bachmann cars are a little smaller than On3 cars, as you might have seen in your post about coupler heights.  On30 was designed from Dept 56 standards for under the Christmas tree displays of their villages, so they chose HO scale track for larger paired down O scale trains, thus the 30" instead of 36" between rails.

In the buying cars world, two things can happen.  When you buy an On3 model, the couplers are a but higher.  This is where you have to choose to go with Bachmann's standards (HO scale coupler height) or On3 coupler height.  If you get an Kadee coupler gauge in each scale, you can easily see the difference (although you are familiar from your San Juan Car co Build).  

I have decided to go with the On3 coupler height on my equipment.  Getting there can extend anywhere from raising truck heights, raising coupler pockets (such as on my BLI C-16 where it takes a little surgery but it can be done...The nice part is the coupler pockets are in soft metal and can easily be grinded out), removing coupler lowering spacers (found on Accucraft On30/On3 cars...They come with the spacers pre installed for the HO height, but you can easily remove the spacer to achieve the On3 coupler height) , or if you are really brave, Wiseman models sells a coupler extension piece that can be added to an On3 height coupler to allow it to couple to an On30 height coupler (it has a knuckle extender that you have to do some work to install).  

I only go with the On3 height because I have some larger K class locomotives from Mountain Models that has On3 coupler heights built in and when i went to lower them, they looked a bit strange.

If you buy On3 railroad cars, which I do quite a lot of (sometimes they are much cheaper than most On30 cars for some reason) they can be very easy to modify if you use On30 standard heights because it is always easier to lowler the to raise coupler heights.  I have found some issues when raising Bachmann couplers simply because there is not enough plastic that remains to make adjustments.  

Remember, it's all personal preference.
Daryl