The bridge is likely a Nashville TOM, not an ABR-1. If it is an ABR-1, you probably have a '61 Reissue, not a Standard, and I would not touch it. Personally, I'd get a Junior or Special and convert to humbuckers before I would take a Standard and convert it to a wraparound...but whatever floats your boat. It's not like it's a precious antique or something. I just don't know what you are hoping to achieve.
You'll have to plug the stock holes and drill new ones, unless you can find someone out there who makes a drop-in conversion (not likely). You can use whatever angle your bridge already has, or if you get a tunable wraparound, you can even put it in straight. I'd just use the angle that is already there. I've seen '60's ones that were angled, and others that were straight, so either way you do it won't be glaringly inconsistent with what might have been. (But those empty stop tailpiece inserts will be.) And the post holes in your pickguard are angled, so those will be covered up better if you keep the same angle.
The '70's and early '80's Gibson bridges could be non-angled because the bridges they used were so wide. Even then, some of them (like the one on my '83 LP Custom) had multiple post holes on the bottoms, so you could angle the bridge if needed.
Doesn't make much sense without an added vibrato, but what they hay?
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