Actually, I'm using the amount of detail put into the AP Class 40 as inspiration for mine. Of course there is not much detail yet, but I hope to cover each and every variation of the Blue and Green era.
However with a loco with that many minor body differences, including 5 different headcode patterns of the same era, I can't use body textures in each asset, that's 2 x 2048x2048 textures for each of 30+ variations! I may have to make a base asset with changeable nose ends, optional vents, plated footsteps, etc. to keep the texture count low.
But for your loco projects I can't imagine you doing that considering that each Indian Rail loco runs into the 1000's and each and every shed seems to want to do their own minor tweaks and of course, liveries!