Engine / gearbox swop

[Jerry]

I need automatic transmission pn my P4 60 due to a knee injury. I cant find any suggestions or advice as to what gearbox might work with the existing engine, so have come to the conclusion that I need a complete new engine and gearbox from a more modern car. I don't want a Rover v8 (don't need the performance and too heavy anyway). Am starting to think about a Mercedes engine from a 1990's model ( bulletproof and readily available). Any thoughts on this would be welcome.