I run the mugen prospec aluminium stock clutch system on my MBX5, depending on the off-road surface I play with the clutch spring to advance and/or delay single or multiple shoe engagement. On loose ground I run 0.9/1.0/1.1 spring, sometimes 0.9/1.1/1.1 other times 0.9/1.0/1.0 depending on the surface. It is cheap and effective for me. I run the Kfactory ventilated bell to reduce generated heat.
There is a new product which you can tune the clutch spring with the help of set screws.