I have 2 Shay's. One has 6 screws in the motor blocks and the other only has 4. What are the product dates or times for each? Did they come sound equiped?

 I have 2 of the 36 (38) ton 2 truck shays and they are different from each other. One has the 6 screw trucks and the other only has 4 screws. Both seem to have sound onboard but I have no idea who's. One of the loco's has the rear headlight mounted on the cab roof while the other is on one side of the fuel bunker. What I would like to know is how many versions of this loco did Bachmann make and at what times.