So I guess another question would be does the YJ 2.5 block mounts interchange with either of the AMC/GM 4 cyls used in the CJ. (like the 4.2 and 4.0 does) I think the GM 4cyl went into a 7 in 1980, so your 79 would need later CJ 4 cyl mounts IF it did swap.
I would only do this swap if the CJ was a 4cyl and I wanted to keep it and gain the later YJ 4 cyl for its fuel injection.
I guess you know about the t-case offset and the axles not going to fit...
1975 CJ-6 1983 CJ-8
1986 CJ-7 Laredo 1986 TJ-7 Trail Jeep
2003 Inca Gold TJ Rubicon