I've put a few Weber DCOE carbs on Spits of various description. No real
problems with clearence either with the side of the inner fender or the
bonnet. Take a look at http://www.team.net/mjb/mark1_weber.jpg if your
internet access is web capable. With a TWM manifold on an 1147 motor, a
DCOE carb, 40mm air horns and an ITG 50mm filter, there is room. From the
port face of the head to the outer surface of the ITG filter, total length
is just under 12 inches.
And the pair of DCOE carbs on the Killer Spit shares the same overall length,
with a Triumph Tune dual carb manifold, same 40mm air horns, and another ITG
filter, on a custom backplate. Again, no clearence problems with this setup,
in either a squaretail or roundtail body.