The TT has a swept-back front needle -- it keeps your pinkies away from the prop very effectively, but you would have to drill a hole in the cowl -- no big deal -- you'd have to do it for the OS rear needle as well.

As for power, there is very little, if any difference between the OS & the TT with a pitts muffler. With the stock mufflers, the OS has a power edge because the stock TT muffler is an interesting blend of high backpressure & high noise. If you put the OS AX muffler on the TT, there is essentially no difference in power. Interestingly, the same thing happens if you put the AX muffler on an old OS 46 FX.

You can fix the TT backpressure problem by removing the baffle & drilling the outlet stinger to the next larger drill size -- that really wakes the TT up without much increase in the noise level.

You can also fit a Tower muffler to either of them -- the output would be virtually identical in that case & they would both make entertaining growling & howling noises.