Upon further reflection, perhaps the Mustang II front subframe wouldn't really solve much in the clearance department. The PV's front structure consists of two hefty spars that attach to the firewall and extend parallel and straight forward all the way to the front of the car, just behind the front sheetmetal where the sway bar, bumpers, and radiator mount. The 544's front suspension sits to the outside of these frame rails - the rails don't go over and around the upper inner pivot as on a 122/1800. So swapping a different subframe/front suspension in would not change the room between those spars. If there isn't enough room between those spars for the V8 then you'd have to replace them as well as the crossmember, with some new structure tied to the firewall/body extending all the way forward. I don't --think-- anybody who has put a V8 in a PV has gone to that much trouble, so I suspect the V8's are narrow enough at the bottom that this isn't an issue.