I have 3 of the FWD engines. As I understand it the only difference is the blocks - specificallty where/how the motor mounts bolt on, and the material the heads are made from (FWD=aluminum, RWD=iron). Supposedly heads, manifolds, accessories, everything will swap between the RWD and FWD versions - everything but the motor mounts. Also the D vs DX block designation only applies to the 350cid V8 as i understand it.

BTW, the 350cid V8 was NOT a converted gasser. It had a completely different block, heads, pistons, crank, rods, and cam - all specifically designed as a diesel components. What it did share with the 350 gas engine was some of the TOOLING for the heads (location, size, and placement of the headbolts) and the block (cylinder & cam bores). This was done to save money by using the same production line for machining the blocks and heads. They also share the water pump, oil pan, timing chain cover, etc. for the same reason.

Although the number and size of the headbolts was enough to hold the compression of a gasser, they couldn't stand up to the compression of the diesel - which made headgaskets their main point of failure. Racers like the diesel blocks and cranks because they can swap a set of gasser heads and pistons into them and have an EXTREMELY strong reliable setup that will hold up in a 600-800 HP motor without having to do anything else to strengthen it.