Would I be crazy if.....

I have a 89 XJ, 4.0, BA/5, 4WD. The block is cracked beyond repair and I have one out of an 88 model that I was going to rebuild and drop in, but now I'm thinking (dangerous I know) about a complete drive train swap out of a newer XJ. If I can find a newer wrecked one with an HO engine and I have the complete vehicle as a donor, how hard is it to swap over? Is there a lot of work under the dash?

I have the plenty of time, this is a toy not my main transportation.

Thanks,
Tom