I kept the origanal tank in mine, just removed the old 5/16" return line and opened it up and put a 1/2" steel tube down through it. And if you get EFILIVE you can re-calibrate the fuel guage to work with your existing sending unit. I persoanlly kept my 95 cluster to avoid many of the associated tasks that came along with swapping the cluster.
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.