Re: T-18 to a YJ 4 Banger??
Ozark is right about the YJ 4-cylinder. The GM engine was only used until 81. The thing to check into is if the YJ uses a crank position sensor mounted on the flywheel since they are fuel injected. If it does, you would have to fabricate some sort of pickup on the 258 bellhousing. Check with Advance Adapters on using a T18 w/a YJ 4cyl. YOu don't necessarily have to buy their parts, but the conversion booklet should have the info you need and it's free.
'75 CJ5,258 w/Howell EFI,T18a,4.27's,33's,On-board air,Warn 8274