Putting an older block might be a problem for 2 reasons, I think, but maybe someone can correct me if I am mistaken. First, I believe the crank on newer 302's is lighter than on older ones, and this may be problem your ECU will not forgive you for. (This is the one I am not sure about.) There may be issues, too, regarding the transmission type, but that is just a thought. The thing I am reasonably sure about, though, at least in the Peoples' Republik of Kalifornia, you can't go older, due to smog laws. If the visual inspection looks the same, ignition, vacuum, exhaust, emmision stickers in their proper place, it might not be an issue, but sometimes the tech's crawl under and check the numbers for things like this. Ford numbers are no secret to figure out, so it might be an expensive lesson. It wouldn't matter if you passed the sniff check if the motor has been altered to an earlier version. Check with your local emmission shop and learn what your options are for your area. I don't know what ever happened to the "don't ask, don't tell" mentality, but ... I hope it works for you, and I would do as suggested eariler, drop in the spare, then rebuild the Fuel Injected motor the way I want it then swap it. Before I got married, I used to have a spare engine and transmission in the garage, "just in case." My friends did, too, then as we had kids, well, spare parts became the "new parts" and the old ones became "core charges". Oh well.