Superhatch

Fresh Z6 swap into a 91 RT4WD. When I turn it over it turns for a brief moment then thunks. Then every turn over after that is just a solid thunk sound. I turned the crank pulley by hand with no problems. Smooth and no noise. After cranking the motor by hand it will do the momentary turn over when starting with the key, then thunk sound again every time after.

My car is at my Dad's garage so he is going to verify all the part numbers off the Exedy boxes to make sure I got the right clutch, pressure plate, and flywheel. The clutch is obviously correct because the transmission shaft went into the splines. I would assume that if the flywheel was wrong I wouldn't be able to spin everything smoothly by turning the crank via the crank pulley bolt, and if the pressure plate was wrong it probably wouldn't fit the flywheel. All were sold together as a 89-91 Exedy clutch kit/light flywheel pack.



^
The Z6 and A6 starters (or at least the one that was in my car with the A6, and the one on the Z6 when I picked it up) look exactly the same, but do have different model numbers. I've tried both with the same results.

I didn't notice my dash lights dimming, but wasn't paying too much attention to them. My A6 starter worked fine on Friday when my A6 was last in the car, and the battery has been drained once, but worked flawless since.

Two bad starters?
Bad battery?
Other ideas?