There definitely was/is a GM 5.7 diesel!!! They were a converted 350cid gas-burner but the block was
A. beefed up
B. machined for the fuel injection pump
C. 4 bolt mains
D. heavier duty crankshaft
E. reworked heads to accept injectors
F. larger head-bolts
very few of these were very dependable and many have been replaced with 350 gas engines or 6.2 diesels
of note GM also converted to diesel a smaller V-8 that they placed in some cutlass's I don't remember it's liter size
spec's would be in a Motors Manual from late 70's or early 80's you might also check alldata online