Sorry, but I have to ask..
why use the front rim? if you take a rear rim (you can install a hub with drumbrake and a sprocket and be set?
the front wheel is indeed difficult, very litle room to work with, especially when it's the one I have in mind (the drumbrake fills nearly all of the rim dish..?)
And why the left side?
put the sprocket on the right (the side that's not already populated by the brake drum) and flip it around.. it's still a front wheel so it shouldn't care and the sprocket would then end up on the left side of the bike too...
you just moved the drum out of the way.
then mount that rim to an axle, rig up a pen holder and draw a circle by spinning the wheel (pen mounted to the same rig as the axle).
Just make sure to pick a good diameter for that circle (one that you can get sprockets for and one that does NOT touch the brake drum side wall!)
it's okay to drill into the brake drum as long as there's enough space inside for your bolt heads so that there's no interference with the brake shoes (check that first!)
drill four holes to install some bolts, a spacer (four tubes to slip over the bolts and four plates to align and fix the tubes welded together) to move the sprocket out and you're done
Still.. IMHO the rear rim is a much better choice!
'sid
