If I were you I would think long and hard about swaping that 2.8 for a 3.4 You can search for info on the 3.4 swap. I've heard good things about Jasper, but you may want to see what other people have to say about them. I know they are expensive though ($2500.00 for a 3.4 s vin block) I'm assuming they will take your 2.8 for the core since the are the same block, even if they say they won't they may not even realize they are not the same before the cut you a check.

91 LS Trooper 3.4 w/225k
BillWhitbeck@grovesigncompany.com