I would certainly guess the 645 springs were simply long in the tooth and there's no evidence that I have ever seen to suggest that a 945 magazine spring is different in any way whatsoever from a 4506 spring. Of course, a 645/4506 could be separated by a couple decades of production, they certainly could have evolved over time.

A Liebenberg 1911 is an -extremely- rare bird, I wouldn't guess there to be but very few in existence, it certainly is no manner of an "offered product" by a large scale manufacturer like Performance Center pistols. And while Liebenberg was obviously the driving force behind the PC, there is (perhaps likely?) a lot that came out of the PC that may have not had anything to do with him since he left the PC before the PC was all shut down.

There's so much mystery behind the Performance Center, I would totally love a huge book (size of th SCSW4) that was ~100%~ about the PC but I fear such a gem may never exist.

In any case, no -- myself, I would not consider a Pistol Dynamics 1911 to be a PC gun but that's just my opinion.

I would love to hear more about that pistol for sure!