Spring relocation kit?
With a stock A-body rear with the offset shackle kit in an early a-body I can run a 15x8 with 5.5" backspace. I'm currently having my wheels custom widened to 15x7.5 with 5" BS because it will cause the section width to be just a little bit smaller than a 15x8 rim. It drops the 275 series tire section width from 11.3 to 11.1. This would give me less than 1 inch to play with on each side. That is cutting it really close for my comfort and safety level. I may need some very thin spacers to push the wheel out towards the wheel lip to even things out due to the offset on my wheel, which I think is around 5-10mm. I may not be trimming or rolling my wheel openings because I have trim on my Signet. If I think it is possible I may trim the molding and the lip 1/4 in. Not sure if it's worth the effort yet.
The other thing you have to account for is that the spring perches were not always perfectly centered on the axles. When you weld on the new spring perches you can get it pretty close to exact. Mine is about 1/8 inch off side-to-side. I think you will have a much easier time getting 275s to fit in your later a-body than myself or '64 Cuda in a 64-66 a-body.
The offset kit was really easy but does require some cutting of the frame rails to clear the welded nut on the front hanger that sits against/into the frame rail. I like having more wiggle room and a 255 will have zero issues in my car. The 275 in my car???? the jury is still out until I get my wheels back.
The nut is inside the frame rail in this picture.
You do weld new perches on for those that asked
This was a 205/60/15 with 3" BS. I have an extra 2 3/4 inches before I hit the springs.
With a stock A-body rear with the offset shackle kit in an early a-body I can run a 15x8 with 5.5" backspace. I'm currently having my wheels custom widened to 15x7.5 with 5" BS because it will cause the section width to be just a little bit smaller than a 15x8 rim. It drops the 275 series tire section width from 11.3 to 11.1. This would give me less than 1 inch to play with on each side. That is cutting it really close for my comfort and safety level. I may need some very thin spacers to push the wheel out towards the wheel lip to even things out due to the offset on my wheel, which I think is around 5-10mm. I may not be trimming or rolling my wheel openings because I have trim on my Signet. If I think it is possible I may trim the molding and the lip 1/4 in. Not sure if it's worth the effort yet.
The other thing you have to account for is that the spring perches were not always perfectly centered on the axles. When you weld on the new spring perches you can get it pretty close to exact. Mine is about 1/8 inch off side-to-side. I think you will have a much easier time getting 275s to fit in your later a-body than myself or '64 Cuda in a 64-66 a-body.
The offset kit was really easy but does require some cutting of the frame rails to clear the welded nut on the front hanger that sits against/into the frame rail. I like having more wiggle room and a 255 will have zero issues in my car. The 275 in my car???? the jury is still out until I get my wheels back.
The nut is inside the frame rail in this picture.
You do weld new perches on for those that asked
This was a 205/60/15 with 3" BS. I have an extra 2 3/4 inches before I hit the springs.