Who knows where they get the rotors. They probably contacted one of the overseas manufacturers direct and ordered a run of the BBP rotors drilled with the 5x4" pattern, or ordered the rotors as blanks and are adding the pattern themselves. Order enough product and this is possible. Looks like they sell the rotors by themselves too, so you could order replacements if you needed. Again, assuming pirate jack is still around. I'm assuming they ordered the rotors blank or with the 5x4" pattern because the pictures they show don't show a dual set of patterns. But maybe the real rotors have both patterns, I haven't seen the rotors in person.
And yes, you could just buy a set of the 73+ rotors and upgrade to the 5x4.5" pattern later. Everything shown in the Pirate Jack kit is just reproduction 73+ mopar parts, they just add the ball joint adaptors so you can use them with SBJ UCA's. And the rotors with the 5x4" pattern.
On that note, you could get everything but the generic brake booster and 5x4" pattern on the rotors from Dr. Diff.
