Might not be what you need to know but bear with me... Some 40 years ago I was given a pair of air shocks by a friend that I believe were for a B body and they had a smaller i.d. eye on the top. I was working at a machine shop at the time so I pulled the upper shock studs and Turned them down. Stupid, I know put I was a kid making minimum wage and couldn't pass up Free shocks. Anyway, I still own the car and am in the process of getting it back on the road. I bought new studs and am looking for shocks myself. I have a '72 Demon and should use the same shock as your '73. Both eyes should be the same size. If not... could someone have done the same to your upper mounts? That's way too hard to believe. Still, both the top and bottom mounts should be the same size, I believe. I will say, your upper mount does look a bit different than mine but looking up shock part numbers, they should take the same shock. Hope you get it figured out... Blessings.