The '58 Squarebird uses a stud upper mount and a cross bar lower mount (as mentioned in previous posts).
I wouldn't call it an 'advantage' but air shocks can be pumped up to 150+psi. They are NOT the same as regular shock absorbers because they can lift over 1,000 lbs., in case you need to deliver telephone books or sand.
Monroe offers the MA763 air shock
Gabriel offers their 49105 air shock
Both models have upper studs and lower cross bars but I would err on the side of caution and try them for fitment because air shocks tend to be fat due to their reservoirs. I don't know if the cross bars are closed or forked but I have a handy angle grinder that makes them all forked. - Dave