WHAT TRANSMISSION COULD REPLACE UN1 ?
The 2 workable solutions for someone to actually offer a kit for Esprits to replace a UN1, rather then each person having to custom fabricate a solution each time are:
Option 1 the cheap, plentiful and robust enough for this application is the Audi FWD 6 speed boxes.
Option 2 is making the Boxter gearbox work in here. Way cheaper then the vintage Porsche options previously used. Plentiful enough and already designed to be mid engined transaxle. Can handle the power, upgrades available, lots of clutches etc...
Whoever offers the first bolt on kit for either of these options would result in a bunch of orders at first and then a continuous stream of ongoing ones as the years went on.