If there's room in there, a Cummins 6Bt and ZF5-42 would work well. I designed a conversion plate to mate the ZF5-42 to a Land Rover LT230 full time 4x4 transfercase (which was then copied and marketed by a Reece Myers in the UK), which i fitted into my Land Rover 101. It was a perfect engine, with good road manners, plenty of power and sensible speed. By making the plate, I was able to keep the transfer case close as the wheelbase of the 101 was short (101")!