Ok, found a very useful thread titled,
"88GMCtruck's 98 Silverado Towpig Build: "Black Fox"
Quote from 88GMCtruck :
GM used 3 BW cases in these trucks. BW1370, BW4401, and BW4470. My truck has a BW4401. It's a predecessor of a BW1370 (they actually share a ton of parts, and half of the case even says 1370 on it). They used the BW4470 in Chassis Cab trucks which were rated at 12,000 GVW. There is also a heavier version of the BW4401, for crewcab longbedtrucks outfitted with RPO 9D6 (11,000 GVW). Both the BW4401 9D6 and the BW4470 use a 1.5" wide chain and gears as opposed to the 1.25", and the BW4470 has a fixed oil pump housing plate which the others do not have. To make it even more confusing up front there are flange (early) and fixed yolk (late) outputs, and in the rear there are slip yolk outputs for early regular cabs, and fixed yolks for the rest.
Haven't read the entire pages, but seems like a wealth of information.
Thanks for your input guys!