The cossie(sierra) used the A4LD box, a basically a C3 with 4th gear(overdrive) added as an extension housing, I used one behind a 2.1 pinto for years, not much in the way of box tune up goodies.
Best people to speak to are ALDERS Automatics, they built the auto box for a customer on his car a cossie sierra with 800bhp, he does use it mainly for 1/4 mile, but they will certainly be able to help you.
The hardest part is going to be the shift itself, as A4LD is vac controlled, but consider making it paddle shift like the auto boxes in ferraris etc, if this can be done to the box, as it certainly isn't electronic to start with would be expensive though.
Another option is to have a manual auto, ie no clutch pedal just move lever.
tabetha