Well, there's way too many steam engines that I'd like to see recreated, but at or near the top of my list would be a Frisco 4100 heavy Mikado (shared parts and some semblance with the 1500 class 4-8-2 types) and a Frisco 4200 class heavy Mikado. There's no calling the 20 4200's beautiful as they were out and out brutes. Trouble was, they pretty much worked out their lives in a seldom photographed area of the Frisco and had pretty short lives given that the road dieselized so darned early, 1951 IIRC. Both types had 27 by 32 inch cylinders and 64 inch drivers. The 65 4100's on the railroad had 210 lb. blrs. while the 4200's had 235 lb. boilers, high pressure for the type.
Lots of good suggestions here.