a 4.0 head will not only fit on a 4.2, it will give you a sig. increase in HP. Here's a link for the head swap and I'd definately swap tires for FI. Just make sure the guy has the complete FI system. There will be a wiring harness and I think you have to run a high pressure fuel pump for the FI system. Anyhow, here's a link for the head.....
85 CJ7 258, borla header, Team Rush, MC2100 ,optima batt, Warn 8274, agr super box 2 & pump, T5 w/ B&M shifter, centerforce 2, superior 1 piece axles, warn hubs 2.5 in lift, 31" BFG MT
85 CJ7 258, A/C, T176, MC2100, Team Rush, Warn XD8000i, superwinch hubs, 3in lift 31" BFG AT/KO