I've given it some thought and if I juggle a few other things around, I can use an HD disc in the REPU.
I had my doubts (fears) about using an HD disc in the truck due to the potential for shuddering while towing, well, launching basically, as occours in my friend's REPU. Dave gave me advice about using a solid tranny mount and maybe a torque brace to help minimize the effect. I have access to competition motor mounts so I'll try those first.
Another problem is the grabbiness and the general dislike for slippage these HD discs exhibit. They are somewhere between a stock disc with marcells and a 6 puck. You
can slip an HD disc for as long as you need and it will take the abuse, but they're not as friendly as a stock disc. Puck, no.
Well, 6 puck maybe.
Now that that's out of the way I feel I should mention how the old REPU setup handled. The disc was almost gone. Friction point at the top of the pedal travel, disc was 6.99mm thickness uncompressed. I don't know how thin it became installed. The nice thing about HD discs is you get what you get. If it measures 7.33mm, as mine does, it stays that way.
Thinner than I'd want, but if you guys think it'll work ok in towing situations, I'll go for it.
Oh one more thing about this clutch issue. My old REPU setup, with its very thin disc, was as grabby as any HD disc I'd ever driven, and even more so than the current setup in my 1st gen RX-7. Man, you blip the throttle just so you could let the clutch out and it wouldn't shudder or bog, but you had to have the right technique. The stock REPU 30 pound flywheel helped in that regard because its extra inertia carried you through while 'finding' the friction point; it turned out my slave cylinder was leaking too, causing the friction point to wander a bit.
Ok, enough of my boring stories. I think I will go with this list of clutch parts:
•Stock FC N326 24 pound flywheel (recently resurfaced at Atkins; this is not a plug; I'm telling it like it is, as the engine was built by them)
•Racing Beat Heavy Duty (HD) clutch disc in 225mm
•Daikin pressure plate in 225mm
•new slave cylinder for 79-80 with rod swapped for old style which is longer for the ribcase style trannies by maybe 10mm