If parts were used from about 3 transmissions could that 3-speed be converted to to add a lockup converter? Maybe the O.D. input shaft & converter possibly the pump, an early 80's 727 lockup valve body in the Cummins 3-speed. It would be like another gear and would eliminate the slushbox feel with those tranys

Probably but, the early lockup converters won't hold the torque. Later diesel lockup converters might not fit in the bell, if they're even compatible with the shafts.

Most guys spend the money on a good tight low stall converter in those applications.

I have trans apart that I'll check out, my truck is just turned up a bit w/15 lbs of boost so I think it would live.

It can be done but it isn't just a bolt in. The diesel lockup converter is thicker by about 1.5" which means the converter sticks out from the bellhousing face about an inch. You need the 2 nd gen trans adapter and starter. The starter hits the frame rail so clearancing is needed there. The second gen adapter is approx. 1.25 longer to fit the converter so the transmission crossmember needs to move rearwards the same amount and shorten the drive shaft. For all that work you might as well swap to a 47RH and get the overdrive as well. You may need a crossmember from an O/D equipped truck but it doesn't have to be a diesel.

The 1st Gen Cummins w/O.D. must not have had lock up? Very good info tho, thanx

Correct, no lockup in the 89 to 93 trucks

I never paid attention to the automatics but owned a few 5-speed 1st gen's years back

The 47RH was a two year only deal, 94-95. You can however convert a 91.5-93 non lockup diesel 518/46RH to lockup with the correct input shaft, reaction shaft (or support) and the lockup valve body. Here is my write up on another site.
Turn a non lockup into a lockup