Here's the one I built (and kept) I built 2 of them, this one from an Athearn
and one I sold from a P2K. They use Miniatures by Eric detail parts. This one was built with a Cannon cab.
Point 1 models made a beauty resin kit of a SW1200rs that does pop up on Ebay from time to time...it is worth it to scope one of these out!
Athearn's are easiest to build, using their flexicoil sideframes, but the body has incorrect louvers and carbody door handles. The SW1200rs had knucklebusters, not handles. The body on the Athearn's is too wide, but the Miniatures by eric (MBE) numberboards fit the wider body and are too wide (but modifiable) for the P2K. P2Ks need you to modify the trucks to accept the flexicoil sideframes.
P2Ks are better runners tho, and their cabs are good enough to not need to build a cannon for it...
The earlier RS's (1200s) had distinct numberboards, step stairs and straighter handrail ends.
The later RS's (1300s) had the numberboards that match the MBE and Juneco parts, vertical GMD style steps, and GMD style bent handrails.
There are 2 diff style stacks too, Juneco makes the eary style, MBE makes the taller and later style.