Norm,
Check out
www.fordbarn.com/forum/showthread.php?t=160532
Or, do a forum search on "retractable 3 point seat belts in a sedan"
It gives a description with photos on how its done. Not a model A but same as Synchro did. I agree, don't try to attach to the wood B pillar since it would just tear out in an accident.
Congrats on making your A driving experience safer with full belt restraints.
Glen