The stroker kit is a waste of time, the I-6 is an awsome motor and is bullet proof, providing it's the 4.2L, not the 4.0L. The price the stroker kit cost, you could have an EFI 350, with much more potential. If you have the 4.3 that is a good motor with decent power, and it is fairly light.
I would drop in a ford 302, or 350SB before I went with the 340. 
and whats wrong with the 4.0
sis had that cherokee for about 2 years, had 190,000 on it and never had a problem, well besides the valve cover leak but thats NBD
got 18-20 mpg and could spin all 4 tires on blacktop
