I have built a pile of these transmissions, if I was building one for my own 727 cummins truck and had to go out and buy stuff and only the best I would get a 48RE diesel core, any gas 46RH core, put all the 48RE guts (rebuilt) in the 48RE front case, the OD clutches, planataries and such into the 46RH OD housing, output shaft and governor with a set of diesel governor weights. Drill the rear support of the 48RE to get a nice tight fit of the governor fluid tubes thru it. Use the 46RH VB, drill out the 1-2 and 2-3 feed holes in the VB plate, turn up the line pressure a couple turns. You will need a little sleeve thingy available at most tranny supply places to fit the smaller LU-OD plug in the bigger RE case hole. Probably missing some details but this would cover the main things. I would want to keep the LU... the non LU trans would run significantly hotter and get worse MPG with all the slipping in the converter from the high TQ especially if combined with high gears, OD and towing.