Its been awhile since I've done any chips, but I believe the calibration for a 4.6 and a 5.0 PCM are very different. Kinda like speaking German to a car that is fluent in English. They just can't communicate. As for finding what tune is on the chip. Back then you would ship your PCM to the shop and they would do the tuneing there and mail it back to you. Don't take all this as from the Bible, there are smarter people than me on this subject. Good luck!
1964.5 convertible and a 2012 Sterling Grey GT. 100 hp. and 412 hp. Go Bama, Roll Tide!