I have Synchro alu cranks that I really like, and that I'd like to install on my recumbent. However, they're 170mm and I need shorter cranks on the bent. I'm thinking of converting the cranks to 150mm by drilling and tapping the new hole to 9/16" x 20 tpi. That would leave about 5.7mm of alu between the edges of the 170mm hole and the 150mm hole. Since I wouldn't honk on the recumbent, I reckon that'd be enough metal left. What do you think? Has anybody done something like that, or should I get new cranks instead?