I would get a brand name diaphragm clutch like Zoom, Hayes, or Centerforce.
If your clutch kit comes with a pilot bushing, do yourself a favor and check it with a magnet before you install it. If a magnet sticks to it don’t use it. Most of the pilot bushings in these kits as well as most of them for sale in the auto parts stores are made in China and adulterated with 40% iron. These cheap Chinese bushings don’t have the self lubricating properties of a 100% bronze oilite bushing. Worse yet many of them don’t even fit! When you pound one of these oversize bushings into your crankshaft you will either shave metal from the OD of the bushing or squeeze the ID of the bushing making a tight fit on the transmission input shaft. Often times the result is a spun pilot bushing after just a few thousand miles.
Napa stores carry a 100% bronze heavy duty pilot bushing. The part number is BK 6151161. Unlike the cheap pilot bushings the 100% bronze bushing is easy to install, won’t gall your transmission input shaft, and will last longer than the clutch. For only $3.29 it is good insurance. http://www.napaonline.com/MasterPages/NOLMaster.aspx?PageId=470&LineCode=BK&PartNumber=6151161&Description=Clutch+Pilot+Bushing
Napa also carries Chinese junk iron pilot bushing BK 6151014 for $1.69. Don’t buy this one.
If you want to install an 11 inch clutch in your Z28 you will need the following parts:
• An 11 inch passenger car bellhousing (GM 3899621, 3872444 or 464697)
• Bellhousing dust cover
• 168 tooth flywheel
• Iron nosed, staggered bolt starter
• Starter bolts
• Starter brace