You are quite right, the Ali viton needles are not suitable for bottom feed - as I mentioned above somewhere. Yes, I am not familiar with TT carbs and all but when you look at my photo below, an Amal I put on the Horex 600 , from the bits I got with the HRDs long time ago : The float looks quite wrong at this angle, did not care about this as I had no angled float chamber then. But even so, NO problems with dripping ! Remember, the float - ahmm - floats in there , so no weight per se on the needle from side loads. So then for saving hassles in your place I´d get some abrasive and the lathe or drill and polish the used needle for a nice cone as it got some ridges from wear. After that just lap it in the chamber jet with very fine diamond paste like 5 micron or any suitable paste. I cannot see why this would not work on your bike. So no real need for complicated mods involving viton bits. In other forums I came across reports about viton needles and dripping carbs, so even with them there can be troubles, just we would not expect them to behave like that old stuff.
Vic
Vic