I have a 96 3500 that is getting tired at 290 k and i have an engine out of a 91 that i bought at a junkyard. I would like to start building the 91 shortblock and then use it in my 96 so i can take my time building the short block and still minimize down time. Are they the same block?what parts are interchangable and which are not?Is there a preferred year or casting for the gen 2 engine?