Hey - cant help on anything else but 7 pin midi is midi + power normally. If you use a 7 pin cable you can normally power things like footcontrollers etc. :)
AFAIK Fryette are not making any of the big heads except the Deliverance MKII's at the moment in any event and the last dealer in the UK that had any were StormShadow guitars who are now out of business.
Getting Fryette (or VHT before them) has always been an issue in the UK.
I'd suggest KSR...
Mark II / III (and the first 503 Dual rectos PT's) were all Schumacher PT / OT's - they are no longer made so if you want exact you would need to pull from another boogie.
The Ampete ones have internal loads for the bypassed amps - setup guide is in the manual here:
https://www.ampete-engineering.com/products/switcher-series/ampete-444/