Parts from the kit before assembly

The two extended hoods means a standard Bachmann chassis block can be used.

You also need some 0.125" x 0.050" "C" section for the new sideframes, some 10thou 0.120" wide plastic strip to extend the cab sides, and a square of 60thou plasticard, 114mm x 30mm for the new frame.

The hood is lengthened by 6mm

Some of the cab front may need to be modified to get the new hoods to fit.

The finished loco at work

The frame is stripped and the bottom section (fuel tanks) is sliced off level with the bottom of the truck mountings.

This makes the chassis lighter, but at least you can see daylight underneath the cab.

The basic structure together. Details will depend upon which loco you're modelling. For a UP yellow loco like 298 I make the structure separate from the frame to aid painting.

Underneath, showing the bottom of the motor. Note the holes for the couplers and to affix the cab & hood structure to the frame.

The chassis back together, a Lenz Gold decoder will fit on top of one of the worm gears, leaving the cab free.

The keeper plates from the Bachmann trucks are sanded down to increase clearance.

I don't see how the Bachmann switchers are NMRA compliant, the keeper plates will foul uncoupling magnets without attention.

American Model Builders cast whitemetal sideframes are used.

My prototype loco, GE 8788 of September 1922, aka YVT's 298.