Re: Spacer out of balance
I've never heard of a spacer being out of balance or requiring balancing. Maybe it's not centered? Regardless it shouldn't affect the balance of the tire because you're only talking about 2.5" out from the center of rotation.
As to the other stuff: A spacer is the way to go temporarily in your case. Disc brakes will bring out the wheel a bit so you'll clear when you do it.
1968 Base hardtop 250 with a P̶G̶ built 2004r
Holley 390 CFM carb
Langdon split header to a 2.5" exhaust