I considered it, but I've drilled 1/4" steel before, and the time, hassle and materials were not really worth it to me; I'm doing too many other things.
You can drill the stock rotors too, and keep the stock brake rotors. But the cobra rotors are better, in my eyes.
Going from Mustang -> TBIRD bolt pattern:
FWIW, I showed up at a machine shop I use for my engine work with the cobra front rotors, my old tbird hub with the studs punched out as a guide, and asked them to drill them for me.
I think I paid $120 to drill 4 rotors and it took them ~1hr (being generous) With their own drill bits.
This is with Bay Area CA labor rates. I'd assume most other places in the country have a labor rate closer to 1/2 that per hour.
In the OPs case, I suspect that with a little more setup work, you could use the mustang rotors as a guide instead of buying the fixture
You merely have to remove the tbird rear hubs and punch out the old studs.
You would then center the mustang rotors in the center of the rear hubs (maybe use hub centric rings like these https://www.ebay.com/itm/4-Polycarbo...-/172382606932
) and finally mark the center of each of holes in the rotor on the hubs.
A decent machinist should have no problems doing that.
They would then drill 5 holes per hub in the spot required to pull/press the studs through. The drilled holes have to be the right size for your chosen studs.
You could then use a nut to suck the studs through the new holes OR just have them press the studs in using a shop press.
If you are friendly enough with the shop, you can probably do the press in yourselves while they drill the holes for you.