All,
Mounting the rectifier onto a chep and easy to get heat sink ( from Maplin or Radio shack) then mounting this directly to the frame wil be much more effective, Between the rectifier use "heat sink" compount to ensure maximum heat transfer.
I have done this on my RC 30 and one of my Ducati's to overcome reg/rectifier problems. The unit runs very cool with this arrangement.
ALL of them use the fram emounting as a heat sink from the manufacturer.
BR
Dvae.