The 350 swap in the Jeep is a whole lot easier and more common. There is tons of information about this swap and a lot of companies produce drop in parts for it. With your 4 cylinder you are going to probably want to swap out your tranny also if you are going to an 8. I know however Advance Adapters make the AX-15 bracket for the 350 though. Wiring harness, emissions, motor mounts, axles (because Dana 30/35 will not hold up to 350 HP 350 Ft. Lb. of Torque), Tranny, Computer etc..... And this is not a complete list by any means, just some big things you will have to tackle.
If you are not at least a 4 out of 5 on the mechanically inclined scale or unless you have the money to have a swap done right then you should look at either swapping in an easier motor like the 4.0 or just turbo charging/super charging your 4cyl.