1/2" will not be enough clearance IMO. I think your main problem is it sounds like you used a different rear brake package "wider" than a stock "A" body when upgrading the axles. I'm just going on memory with that theory, I think factory rear "A" body brakes were 2" or even 1.75".
The 145/60/15 is a oddball size I would go 255/60/15 if it will fit for more tire choices and probably a better price.
How much clearance do you have to the leaf spring from inner wheel?
