How high can the fuel rail be lifted before it compromises the mouting of
#6
If it helps, the greenies use a 0.250" thick spacer, not sure how much more you can go...
but I do seem to remember fairly decent clearance to the bottom of the ypipe (your only obstacle IIRC) & don't forget about the pheny spacers as well; this could also come into play with the bi-pipe.