on the 4.0 your not going to gain anything by port and polish cause your power is being used at low revs. acutally you can make power worse on engines like this with a port and polish. Roller rockers and other such things can help.
1987 Wrangler YJ RED 4.2 5-speed, NP231, BFG 31x10.5R15 AT/KO on 15x8 gambler wheels.
Caution!!! Under construction!!!!!! Caution!!!
Finishing a 4.0 Cyl.head swap, Just got an AX-15 NP231J combo to replace the busted t-case and craptacular BA10/5. Adding Nutter bypass. Probably more to come before it is back as a DD!