I was going to do that myself in my CJ5 and I know it would be cheaper for me to do that, but.... I am going to build up my 258. Well actually, it is a 232 right now. I am going to put a 258 crank in it, put on a 4.0 head and with some stuff from Cliffords, have a hot 258 that will supposedly out perform the 304. Actually the 304 does not have that much more HP than the 258. But good luck with the 304 it is what ever you want. DON'T forget, the AMC 360 and 401 will also bolt up just the same.