i need to get a clutch kit, and zoom is the cheapest i can find, its for an '89 Iroc-Z 305TPI 5speed, i need the clutch to sell the car. but jegs lists two different clutches, and both seem like they arent sure of what they fit, here is the info from jegs website:

PART # 770-MU1675-1A
Pressure Plate Dia.: 10.4''
Disc Spline: 1-1/8'' x 26
Disphragm
Applications:
Camaro, IROC 1987-92 5.7L
Camaro, IROC 5.0L (305F)
Firebird, Trans Am 1987-92 5.0L (305E, H)
Firebird, Trans Am 305F
Firebird, Trans Am 1987-92 5.7L

PART # 770-MU56-1
Pressure Plate Dia.: 10.4''
Disc Spline: 1-1/8'' x 10 <--Summit Lists this as 26 spline
Diaphragm
Applications:
Camaro, IROC 5.0L (305F)
Camaro Z28, IROC 5.7L 1987-92
Camaro 1984-86 5.0L w/10'' Clutch
Firebird, Trans Am 5.0L (305F)
Firebird, Trans Am 5.0L (305E, H) 1987-92
Firebird, Trans Am 5.7L 1987-92

 

I've looked at those zoom clutches more times than I can count here lately while shopping for a replacement for mine. The one you need is 770-MU1675-1A. I too looked on both summit and jeg's websites, and summit's info seems to be all messed up. If you were going to keep the car, I'd recommend the zoom multi-friction unit (part# 770-MF1675-1A), which is really good quality clutch, but it costs about twice what the MU series unit does. If you're just going to sell it, just throw in the MU clutch, which is equivalent to the OEM clutch.