I am not aware that Ford ever made any meaningful improvements to the timing chain cassettes, guides or tensioners. The 4.0L SOHC timing setup is just a pour design. If I were doing a 4.0L SOHC engine swap (which is something I may need to consider in the future for my '01, Job 2 ST, which rattles at startup) I would not install a used engine w/out replacing all of the timing chain components on the replacement engine, not because the quality of the new parts would be any better, but because I believe this would prevent me from possibly having the same TC problems repeated on the replacement engine in the near future. Some SOHC engines have had TC problems with as little as 75K or less. With these engines it is not a matter of if you will have TC problems, but when. Why some SOHC engines fail prematurely and some may get 200K w/out problems is a mystery to me. Lack of maintenance and use of expensive/exotic oil with 3,000 mile oil changes doesn't explain whether plastic parts break or not. Perhaps the way the vehicles are driven has more to do with it... ?
The electronics between engine years may be compatible, but I've read where some of the electrical connectors may be different. You'd have to compare and see I guess. To avoid possible issues with connectors and perhaps sensors, I think it would be safer to reuse your old parts, or use new parts specifically for your original engine. Ford can and does make changes to stuff w/in a single model year. When you're looking at a 5-10+ yr spread, who knows? A good way to check beforehand would be to check RockAuto's on-line catalog for part numbers between years. Even minor things, like the length or how a throttle cable connects, can cause you headaches on a swap. If you purchase a re-manufactured engine it will not come with all the peripheral parts. There's a reason for this.
