I was under the impression that ACDelco was just a re-boxed Raybestos (same casting number) unless you find an old stock ACDelco.
I had problems with the new slave cylinder (tried to bleed the stock one, and the bleeder twisted off) and went through two for the stock getrag, after measuring the bore it was slightly larger than stock.
As you must know the hydraulic system in stock form has just enough movement to disengage.
I ended up using the slave cylinder from the four cylinder vehicle and have quick disengagement.
I was going to drill out the threads from the studs, but just ended up threading the mounting bolts through the slave cylinder into the mount on the transmission.
With this slave at least even if there is a leak, the clutch will still work.
1988 Fiero GT