To the best of my knowledge, I believe the 3406B model blocks were the same. {3406B ; not 3406A or 3406C models) EDIT :NOTE: I'm talking cast iron blocks ONLY; NOT any pieces inside that block !!!!

I'm uncertain when they changed to the rear housing (and rear casting of engine block) from the old standard 19 bolt hole design, to the newer 24 bolt hole design, but I think it was on the 3406C model.

On crankshafts, there are some difference, between each model; 3406A front c/s gear is different than 3406B model front c/s gear.

Right after 3406C model (3ZJ s/n prefix) got introduced, then CAT went to a wider rod journal crankshaft design; Our old service salesman tried really hard to track down the closest serial number range and the best he came up with ,was that at roughly s/n 3ZJ02340 and above got the newer design crankshaft (with wider rod journals)

I don't know enough of all the particulars, for the cylinder heads  to give an answer(valve stem materials; updates done to cooling passages at rear of cylinder head above #6 cylinder exhaust port area; 460 HP cylinder head was different = precup spacer height differences) These are a few that I knew of.