Whoa that’s a big tire for that cam and stock stall
Yes, that is a zero balance converter or neutral balance.
I had that exact issue with my wife’s’67 Cuda and the 904 I came with. It had the odd spline count. I found it impossible to get even a replacement converter never mind a performance unit.
So! Down the block from me (Literally) is a converter shop called Pro Torque that custom re stalled and built up the OE converter. Expensive but worth it. Lots of ceiling room. Perhaps that idea is a workable solution for yourself. A capable & Local shop?