the spline locations between a t-350 and the t-350C are in different locations as you have learned. Both input shaft and stator support
If you cut the polished nub off to move the converter more towards the trans... you push the converter drive hub into the pump gear and can push the gear into the surface of the pump cover. So the next failure will be the pump.
At that time you can repair the t-350C , then buy the proper converter or convert the t-350C to a non lock up setup.. That requires parts from a non lock up t-350
Some people are like Slinkies... Not really good for anything, but they still bring a smile to your face when you push them down a flight of stairs.