Swaps done over here include Jag efi 4.2,3.8, a few big V8's, BMW 2.5 TDS, Cummins civvy 5.9 BTA (+ non-turbo) Deutz air cooled 6 cyl, Steyr MI16 and the old Perkins lump.
I could never get my head around why MoD would choose an engine, then redesign it to lower the power output (ie CVRT, Warrior,Challenger etc). I think J60 was detuned from 265 down to 195 (ish)horse, oh but then its got to drive that huge mixed flow fan...and a thumping great alternator....and then lets put it in a very tight fitting armoured box at way above acceptable running temperatures. After all that it was no wonder poor squaddie had to drive it foot flat to the floor! Case in point-MoD upgraded CVRT to the cummins 6BTA, then detuned it to match power of the J60! Mine was a bit gutless, so I tweaked the fuelling at war & peace (see you tube clip-PKE646L). not ideal, but I was only copying VW's idea....
A replacement engine needs to have a min rev max of 4750 to make 50mph (higher is faster) 240 or more horse and must have minimal torsional vibration-the thump on the drivetrain. This counts out many diesel engines, petrols are smoother.