I have a civilian Willys with a Buick v6 conversion. Clean way to go(I must add this is a scratch built jeep not a modified original). Can even use stock CJ parts from the 60s, clutch T-90 etc, as this was a stock Jeep v6 in the CJ-5. This engine weighs in as much as a Ford small v8.
225 Buick odd fire in M38 w/TH400 trans Dana 20 xfer and Advance headers, power 4wheel disc brakes, power steering (saginaw).
225 Jeep (Buick) odd fire in 47 2A with T-90 Dana 18 xfer and stock jeep exhaust manifolds, stock brakes, steers hard with stock manual linky link steering.
Also the Chevy Vortec v6 with fuel injection would be my choice, it is very powerful and reliable..
I do prefer Stock WW2 jeeps!