the 735i was the last manual 7 series in the us, and was in the e32 chassis. the 4.0 & 5.0 were both autos.
the e38's did not come in the north american market with 6's, or manuals. however, a 95 e38 740i (not the l chassis) can be (and has been) swapped over tp a 6 speed manual from a 5 series. it will fit, and the driveshaft and the rest of the parts are all oe parts, so no 'custom fabrication' would be needed.
there are lots of threads on this on the internet.
swapping out a v8 to run a 6 is silly. your options for this are the m20 (too old...), m50/52 (too slow, just drive a 525 and you'll see...), s50/52 (too expensive to do this sort of swap anyway...why pull out a stock 300ish hp for a smaller inline 6 with about the same horsepower but will need 3x the $ in fabrication/programming for it to work properly), an m30 (less horsepower, about the same fuel economy as a v8)
so in a nutshell, keep the v8, look for a non 'l' chassis, and do a 6 speed swap. a 5 speed may also work, not sure though. i believe the 7's all came with a 6 speed in the euro models.