Whether or not it's sacrilege to cut off the downtube bosses, I'd be pretty concerned about weakening the frame at this point - I once tried the same thing on an old 531 frame and was left with two holes and a lot of daylight at that point, plus a scrap frame - lesson learned! I'd suggest buying two domed rubber tap (faucet?) washers at the hardware store deep enough to cover the bosses. Drill the centres out to the right size and put the screws back (slightly countersunk) and no strength is lost - and you won't rip your legs in the event of a tumble.