Guess I'm getting locked in on a decision to go ahead with the F100.
My son is ready to let me buy it. We're hoping to get it moved here a week from tomorrow.
Talked to the manager at LKQ salvage yard that's a few miles away. He has a 2WD Expedition with 5.4L Triton that hasn't gone out in the yard yet. It has 180K miles on it but runs quiet and smooth, no valve or other worrisome noises and smooth exhaust out the tail pipe. Engine was quite clean externally but the oil was dirty.

Transmission fluid looked new. Wish I had checked the oil pressure. (always forget something!!)
He has a few Explorer rear ends. I can get the engine, transmission, PCM, harnesses, sensors and gauges and a disk brake limited slip Explorer rear end for what I think is a pretty reasonable price. I believe the engine is usable as is. Need to check the transmission. WXO and I will go back and drive it around the yard to see what's up. There has to be some reason the truck is being scrapped. If the engine needs rebuilding somewhere down the line, so be it. That would be a good opportunity to add some HP.
Don't think he has the '03 or newer Crown Vic steering and suspension but his price was high on that anyway.
Ordered a temp, moveable 10X20 plastic shed (thanks for the suggestion, WXO) that will serve as storage for parts (engine, trans, fenders, hood, aprons, box, ...) now and as a paint booth later. When its no longer required (yeah, right!!) it can come down and itself be stored.
Feels good to be moving on the project.