'73 Disc conversion, but keep 4" bolt pattern

The pirate jack stuff appears to be all 73+ parts. If the pictures are accurate they're 73+ spindles, that's why they need ball joint adaptors for the small joint UCA's. I'd wager they're having the rotors shipped blank and drilling the pattern themselves.

But yeah, just getting the 5x4" bolt pattern isn't enough. The 73+ hub register is bigger, the track width is wider, and I don't know if those are 7/16" studs. They probably aren't, but I don't know for sure.

Of course, the SBP wilwood set up has all the same problems. Track width, hub register, and stud diameter. Might work if you have aftermarket rims, but most of the OE wheels aren't going to work.