I had a short glass pack on the first truck i ever owned an 82 s-10.. sounded pretty good single in dual out.. but, than again i was only 16... so.. you know how it is when your a teenager anything extremly loud sounds great - i'd go for the longer ones as well - when i had my 96 dodge ram it has a driveshaft out of a big-rig under it that was sawed off on both ends cut down to about 3-4ft and that was its muffler it sounded great deep toned etc but i traded the dodge in for my yukon.. it has a Ravin exhuast on it didn't cost that much like 40 bux for the muffler.. what cost me the most was having a Y pipe built to go from dual to a single in muffler single out - but that was my pref - i'm assuming your doing dual in dual out? it should sound pretty good get the longer glasspacks to keep it low toned
--edit--
Umm.. i forgot your driving a TBI truck, so i don't know how the exhuast on it is, i don't know if it is single all the way back or dual all the way back to the muffler..