The 26" unit we made was patterned with a B and E body. I don't think we ever got our hands on a 73 Valiant with a 26" radiator support. However, if you have an original 26" shroud, I think it's going to be an easy bolt on. You might just need to drill holes in the rad brackets to mount.
If by any chance you or anyone else has the original radiator, we'd love to be able to borrow it so that we can make a specific 26" A-body unit that is a true bolt on.