A friend had a XJ V12, blew a head gasket, cracked the head. So, a big block 454 with rv cam was installed backed up with a 4 spd auto. Had about 2 inchs of ground clearance. Installed a set of Perellies. Had to reverse the manifolds. At 80 mph we could get 22mph in 4th gear. Installed throttle body injection. We had alot of fun. Took it to Canada on a trip. Going up I90 in the middle of the night, drove really well, speedo buried. Car weighed about 4k. Lots of fun.
I had 3 XJSs. Drove them a combined 100K without a repair, while my friends’ Porsches, BMWs, and Mercedes lived in the shop. Love Jaguar. My only Porsche was a daily nightmare.