Turbo spline is the only way to go.
BTE does NOT recommend a powerglide spline in a high HP application, they are WAY to small and will snap like a tooth pick.
Like Zip stated, you either have a turbo splined converter or a glide splined, you cant have both, if I had to guess, your converter is turbo splined.
Most converter company wont even make their converter in a powerglide spline unless you ask.
Cp