I also had a bud with a 69 firebird and the 250 ohc, it was a great car, but as usual, he wanted a v-8. whaever, I liked it, my brothers had Xk140s and XK-e's (coupe and roadster) so I knew that the 6's could be made to go.
I think you should put that jag motor in there - after all - people used to stuff chevy v-8s in the jag sedans all the time when they got sick of lucas electrics, waiting for parts, etc.... :p
