The later model transmissions were just updated with better parts, bearings instead of bushings etc. The valve body and tcu changes were just better shift quality. New or old it does not matter the transmission in stock form can only hold so much. As far building it to handle more power I would suggest just having it done. You need to add clutch packs and by the time you buy or modify the parts to do it it is not cost efficient or get a v8 transmission and tcu that will work with your car and change the final drive ratio to match. Still not cost efficient. The only cheap things you can do to increase the power handling is an upgraded valve body or just the blue to solenoids for pressures. This makes them shift very harsh though.
Torque management will not handle all of it for you.
I would advise going in and replacing the k3 clutch pack from one from a v8 and then adding as many clutches with the thinnest steels as possible on every other clutch pack if you want to do it yourself. Then set the clearances as tight as you can that they do not drag to much. Put the blue top solenoids in and it should hold together for a while.