As Myles says, with my powerspeed system on the K there is about 30mm from No 1 primary to the alternator.
I've wrapped the primaries with the cheapest wrap product from Rally Design, about £20 for 50' of 2" wide. Under bonnet temps are now much lower, with a corresponding increase in the temp of the unguarded silencer.
Cheers
Tom
FH54WLX
see here - UPDATED again