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
Dont worry how old you are... it is the mileage on your body that adds up.