the cheap heavy duty option for L16-L20 is a Datsun Sports 2000 clutch - bolts straight on. That's what I used on my old racecar and never had a problem.

I would speak to the clutch specialist and see what the have to offer you for what you want, they might even make something up to suit.
I would recommend a super heavy duty pressure plate to give you a nice hard pedal (being hydralic) and then a jap clutch plate. keep in mind when its all too tuff something has to give (gear box) (diff) etc. i would preffer to burn a clutch plate from time to time than any of these.

Its time to upgrade the clutch behind the stock L20b and I need some specific suggestions.
A friend told me that heavy duty covers a very broard range .
I may go to a stroked ex rally L20b motor. So it would need to have enough clamping pressure to cope with that.
I'd rather not spend thousands on rocket ship stuff. I just need a strong reliable unit siutable for drags and street. Cheers