Mozz hit the nail on the head. They were different blocks. And I'll admit I'm not too well versed in the inner workings of them. I too thought the 427 was strictly a Chevy or GM product. But this owner said something about the heads being different, maybe taller or something like that. And the reasoning also had something to do with the ability to fit these things between the shock towers in the front.
Plus Ford was one of the first to start that damn unibody type approach af welding the entire inner structure together. Made engine work and engine swapping a real chore. That was the beauty of the GM's. The ability to remove everything from the firewall on forward. That gave easy access to the frame and engine mounts.
Heater cores and A/C evaporator cores.................. I do quite a few of them in my business. I guess it really started when they first started converting from R-12 to R-134
I took classes to learn how to do them. Then it became almost natural to continue to do Auto HVAC to recoup some of the investment in the training. It seems like I get the tougher cases to repair. Last summer had to do work on a Honda Accord. Heater core leaking so customer wanted both cores replaced since the evap core had to come out first. Owner also complained of AirBag light was on. Honda in their infinite wisdom placed the airbag control computer under the heater core. So when the heater core leaked, it went right into the computer. And we had to remove most of the dash for that job as well.
Monday I'll tackle the wiring on the Mustang. Came to find out that the trade school trained employee doesn't know jack squat about wiring. After 2 days, he's no further along trying to find the short in the headlamp/courtesy light wiring. AAARRRGGGHHHH According to him he needs all kind of testers to move ahead. No jackass, it is a 12 volt system. That was all they used back then. All you need is a 12v test light. It either lights up or it doesn't.
Man these kids of today certainly don't have the work ethic that I was taught. Or the belief of improving one's self in their job !!!!!