This thread doesn't involve a 904 (and I can't think of a reason why the spacer/adaptor wouldn't work to put a '68-up 904LA behind a slant-6, can you?)
The pilot on the 727 converter is the same size as the late (68 up) 904.
Oh yeah, I always forget that detail -- you're right, it was only the pre-'68 904 that had the 1.55" torque converter pilot diameter; all the 727s and the '68-up 904 have 1.8" pilot diameter.