The seller just replied to my email (well his email was full so I made a paypal dispute and he replyed to that) and it gets even more complicated to what I've read from here that 615 friction disk works with 574PP:
"The 88 1861 999 615 [ZF disc] is the ONLY correct match for the 88 3083 999 574 [934/935 PP]"
"615 disc TO 594 pp = NO"

Seller says:
The 615 disk that came with the box is 8.8mm

The seller still insists that 574 is discontinued and IS THE SAME as 594 NOW!
This can't be true, they can't change items (574 to 594 spec) drastically with same #number can anyone confirm this for me?

This is what Sachs online catalog says for that 615 disk:

Utter nonsense. If that seller insists they are the same, he is wrong.

Yes, the 574 includes a 930 release bearing while the 594 does not, but that is not the only difference.
Put the two pressure plates side-by-side and there are measurable differences, not the least of which is the dimension between the friction surface and the perimeter mounting surface.

It you use a 574 with a standard disc, it will drag, never fully release. We went through all this and documented it in Tom's UBER930 build. The combination of the 574 plate + 615 disc successfully held over 600ft.lb. at the wheels on that car and several since.

Is the 574 discontinued? Quite likely it will be, as every year their availability is reduced. It's a motorsports part from 40+ years ago, very doubtful there's much demand to justify the manufacturing expense.

Is my math right? 450nm is about 350 ft lbs of torque? I think the 934's were low to mid 500 torque back in the day. I guess some are lucky to hold that kind of power with that disc, but I have bought many over the years and it won't hold 600+ for me. I guess it may depend on how aggressive your power curve is and how much air flow is going into the motor. 15-20 psi of boost on a turbo flowing 51 lb minute is much different from 2 that flow 60 lb.

*shrug*
It has always worked for us.

Your car sounds pretty aggressive. Are you running the 930 long bell housing 4-speed?

No shortened 930 box with custom gear set. It held ok with twin 48mm wheels, then I had a set made that were 51mm each and if you kept it under 22psi it was good. now I run twin 60mm and 25psi and a solid disc. Hold very well, wouldn't want to get stuck in stop and go traffic. HAHA Tried to get a nice twin disc set up made but no one seamed serious about helping me. Not sure if the shortened bell housing has enough room for twin disc, so if you want to play with the big guys you have to make sacrifices.

And here is the answer straight from Sachs:

One of the three tabs or rings on 574 pp interfere with the top driver side trans bolt? What are those tabs and how is the 574 supposed to be installed?

It looks like they are for some protection for shipping and should be removed.

Edit: Yup, took them off and they released the pp so the tb is now also loose.