Is this a bad idea? If I mitered and brazed an extra tube from the seat-stay to the chain-stay under the disk braze on would that be sufficient reinforcement? I know that many coaster brakes and drum brakes attach to the chain-stays of bikes designed for use only with use rim brakes without problem.
Seems to me that disk brakes are the only difference between a new Surly Troll and a vintage MTB that costs 1/10th the price. I'm assuming I'd also have to spread the rear triangle.