T16 is the easiest as all required parts are available from the MG/Rover parts bin.... VAG , I have no idea of how easy it is to transplant the engine ... ( MG g/box or VAG ? ) if its a VAG g/box its not harder to use a Saab B204 or B234 engine and box ( as I see it) ...The saab will take silly power on stock internals and you can even retain the Saab ECU... plenty of mappers on the Saab forum willing to map for not a lot
all IMHO of course
a 500 or 600 BHP ZS would scare a few Ferraris and Porkers LOL........ and to me thats the attraction