And your '79 case fit just fine without any need for driveshafts work? Must be a NP208 then, those started showing up in Fords right around that time. The usual t-case in the 70s was the NP205, which while very strong is also quite a bit shorter than anything Ford put in their '80s and newer trucks, so shorter front shaft and longer rear shaft are needed for it. Funny thing, our 208 is also a '79 production run, must have the brass parts inside it then - never opened it, so wouldn't know for sure. Won't find any brass in a later BW1356 case tho, all plastic IIRC, but they still run for hundreds of thousands of miles (or till the pump spins and self-destructs into the chain drive). Idk about the 1345s, haven't had one opened yet...
Forgot to mention about the gasket thing, well that kinda depends on the transmission. The T19 stick-shift (and most other 4-speeds) would greatly benefit from an actual paper gasket slathered with RTV on both sides as the rear bearing is wide open into the tailshaft housing and some oil will find its way there thru it. A newer ZF5 stick won't care one bit, that one has a seal behind the tailshaft bearing so whatever soup is in the trans stays there and does not migrate up into the tailshaft housing. When I yanked the T19 and replaced it with a NP435 (again 4-speed but different gearing) I did the RTV + gasket, not a drop of oil ever leaked till yesterday when I removed the t-case. The new ZF5 is only getting a light coat of RTV, mostly to keep the elements out as there isn't anything inside that are that actually calls for a good seal...