I have no connection, but wondered what was available for B, C, D models if an engine upchucked and died. http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=180416827196 There are some out there.
580D can be repowered with a 4-390. requires a new bell housing. Contact your Case dealer about a repower.
I had a D once with the Cummins conversion, very nice machine. That's not a bad price considering what was probably paid out just to rebuild the injection pump. The G188 from the Case 430 and 530 farm tractors will bolt in I believe. The common farm tractor engines don't have the mechanical tach drive, and the 450 dozer/loader engines have a unique oil filter mount that apparently will clear the B frame, by turning it. The 207 and 188 engine was used in the Case forklift too. These machines can be purchased reasonable and parted out for the engine. The 188 can be changed to a 207 by changing the sleeves/pistons, but the engine will still use the smaller rod journal crankshaft( like the early Chev 327 engine), and I'm not sure of any balance issues. The farm tractor block will need the liner counter-bore diameter changed for this conversion. Phil