I am currently doing a 318 swap into mine but researched all other possabillities first. depending on how "blown" the 4.2 is you have a few ways to go. either put the 4.0l in it as-is. Next option, assuming the 4.2 lower end is ok or worth saving, put the 4.0l head on the 4.2 block. this requires reusing 4L header and valvetrain. otherwise this is a normal swap for 4.2 guys who want either fuel injection on an originally carbed engine or want the claimed 40hp increase and better gas mileage. and the third way to go would be putting the 4.2 crank and rods in the 4.0 block and you get the 4.7L stroker engine. each way has thier ups and downs but in essence you can do any of these swaps with not alot of trouble and usually using oem parts. this is what i am trying to do with my 318 swap is use the least amount of aftermarket parts to do the actual swap and also keep from fabbing up too many things from scratch as well. this allows me to go to the local parts house and just buy what i need. just gotta keep a list of the vehicles the parts were for originally. If you have any questions bud we are all here for you.