You could also swap the PROM chip in your 94's ECM to an updated one to work with the new style 5521 IP if your 94 hasn't been upgraded yet. As for the DURAMAX swap, I documented mine here in some detail and theres a few others.
This will give you an idea of how I did mine and what all I went through with my 95 SUBURBAN.
http://www.thedieselpageforums.com/t...ad.php?t=34348
1995 GMC 2500 SUBURBAN powered by 01 DURAMAX/ALLISON, 3.42 gears, 261 T-case
Trans has a mild build with ALOT of help from MIKE L. which included ALTO's for C1-C4 and a PI ML converter
DIAMONDEYE 4" exhaust with a CORSA muffler, AFE stage 1 dry filter, EFILIVE, KENNEDY single pump and pump rub kit.