1st, you need to look at the 4l80e in generations. 91-93 for all purposes is it's own trans. There are several differences in 91-93 vs 94+. Then you have 94-96, which looks like the 91-93, but uses the 94+ valve body. Then you have the 97+ center lube style. Most pro builders stick with a 96- to build, or at the minimum use the overdrive roller clutch out of a 91-00. The ONLY advantage to a 97+ trans is you can add in the sonnax kit to engage the over run clutches in 1st to 3rd while the shifter is in 4th(this is useful for snow plowing or if you frequently get on and off the throttle, and shift from reverse to drive alot).
IF you're dead set on going to a 97+ style, you should also add in 3/8" or 1/2" trans cooler lines and a later model radiator with the higher flowing cooler as the 97+ needs ALOT more cooler flow than a 91-96. At the absolute least you have to adapt your 5/16" lines over to the 97+ style hook-ups(and make certain to use the 4l80e SPECIFIC fittings). Next you have 3 choices, you either re-use your 91-93 style valve body and add in the accumulator housing from it to the 97+ valve body and drill the extra passages, upgrade to a 7427 ECM with a custom tune(the 7427 was used in 94/95, but 94/95 7.4's had high pressure injection vs the low pressure injection of 93 and older 7.4 tbi's, so custom tuning is required, or you have to change the fuel pump, injectors, pressure regulator spring, and I believe add in a 2nd knock sensor), or go with a stand alone trans controller.
Personally I would stick with your 91 trans, rebuild it with borg warner high energy frictions(stock frictions for late model 4l80e's), heavy duty intermediate snap ring, all new bushings, internally dual feed the direct clutch, use the sonnax boost valve with internal bypass spring, transgo actuator feed limit valve, rollerize the output shaft, rollerize the forward hub, transgo or sonnax tcc valve with a sealing ring, new electrical, converter with a billet piston, new style internal & external harnesses if not already done, and a HUGE external trans cooler(LONG makes a nice one for $130 on Amazon). I'm sure I'm forgetting a few things, but there are TONS of write-ups out there on 4l80e builds and proven build combos.
