Hi
Need more detail of what you are after is it the pull on the clutch lever that is heavy, or is it the weight of the clutch assembly that you are referring too, when you say a Manx clutch what are you referring too also, as there a few minor details over the years and also along with plates and with what is being supplied after market.
My Manx has full fibre plates as standard, but ears break off, I have currently fitted McIntosh standard steel and insert plates that give just as good performance, but as I am running the standard Norton box (1955) the lift on the plates is limited unless special things are done to increase the lift on pack to allow full disengagement, can be a pain in the but for clutch starts and clean gear changes.
The increase in lift results in more clutch lever force required.
Commando clutch when properly set up is a dream in my opinion.
Also as mentioned above Lytedrive Engineering work seems to be pretty good, from what I have seen and would be worth talking too.
Best Regards
Burg