I have a Centerforce Dual Friction in my 68. Works very nicely. Very smooth and certainly not too heavy a clutch pedal. The clutch mechanism is all stock C3 Corvette. It couples a ZZ4 Hot Cam to a Tremac 600 five speed.
After I bought my Centerforce, and before I installed it, there happened to be a flurry of postings on CF about people having balance problems with the Centerforce clutch. It's a centrifugal advance clutch. The clutch diaphragm "fingers" have a ring of little counterweights "woven" onto the fingers. The ring of counterweights is moveable, can slide back and forth, up and down, etc. I called Centerforce's technical advice because I was worried about getting myself in trouble with their clutch. They said that the counterweight ring is adaptive, it normally self adjusts and aligns itself to balance the diaphragm assembly.......however, if the engine balance is incorrect.....it will not automatically adjust....Tech advice was that people having balance (vibration) problems with their Centerforce clutches had an engine imbalance problem. Anyhow, I used the correct GM flywheel with my ZZ4 and have no problem.
..The Dual Disk. I have a McLeod dual disk on my 70. I haven't driven the car, so I can't say that much about it. It too is mated to a TKO 600 5 speed. I have the stock C3 clutch mechanism and I guess everything is OK. Except for being quite a bit more expensive, the McLeod mounted up MOSTLY OK....except sliding the TKO input shaft into the clutch. With two disks to mount up too, it was much more of a a struggle than a single disk. The plastic shaft alignment tool, was for me useless. I struggled for a long time with the plastic alignment tool to no avail. I ended up buying a real Muncie 31 spline input shaft ($105 from ebay). With a real 31 spline metal input shaft to align the twin disks, it went it pretty easily. (I think the input shaft is 31 splines...the memory falters.)
.....about the scattershield. My 68 has the stock GM bellhousing ..no problem with the ZZ4 given it's HP rating. For my 70, I'm currently targeting somewhere around 600 hp. This is naturally aspirated with 496/502 cubic inches. I'm planning on using the stock GM aluminum bellhousing. (Actually its the same bell housing as the 68) The GM bellhousings are light weight, and more importantly don't requirement alignment to the engine and bolt right up, since the OEM bellhousings are machined accurately. Shouldn't be any problem as long as I don't do something stupid like rev the engine to 3000 rpm in neutral and dump the clutch. (I've read that the GM Performance Parts repro bellhousings are NOT accurately machined as the OEM bellhousings. One poster said the repro bellhousings mounting holes were drilled 0.020 inches off tolerance.)
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