That Ebay listing says 15 inch wheels req'd. I'll assume 5 on 4.5 LBP too.
You really should change to a dual line disc brake master cylinder and proportion valve too regardless what disc brake system you choose.
If disc brakes is the goal, Scarebird conversion wouldn't change your OEM bolt pattern.
Where 15 inch wheels ( w/ shorter tires of course ), large bolt pattern 1/2-20 right hand threads on all 4 corners is the long range goal... someone else will need those spindles you have and you'll need a LBP rear end.
Big wheels with short tires will cost you coins and some ride quality unless you invest more coins in shock upgrade. There I'm getting into the going instead of the stopping, which is off topic, or is it ?
Now for me personally... I guess I'm lucky to already have all the later model OEM parts to poke under my 67. If I didn't have these parts and needed to do any repair what so ever to the OEM front drum brakes, Scarebird would be my choice. Main reason is, I consider myself too old to set long range goals.
