someone correct me if i'm wrong but aren't these basically a 194/230/250 Chevy inline sixes (GREAT motors btw) with two less cylinders and a crossflow head?
The "Iron Duke" was a pontiac engine but was also used by AMC in the early 80,s and Grumman used them in mail trucks so they cant be all that bad. It had the intake/exhaust on the opposite side from the 4cyl chevy.