One-piece Ashtabula-type cranks used to come in various lengths; 3 1/2", 4 1/2", 5 1/2", and 6 1/2". If it's an old Schwinn the bottom bracket threading is likely 26 TPI whereas non-Schwinn parts would be 24 TPI, complicating things. My suggestion would be to get it to a shop for an up-close look by an old timer, if you can find one.
Barring that, converting to a square taper spindle with the accompanying parts might be easier.
*edit*
Looks like new production, not "real" Schwinn so might be simpler to find something in one-piece.
Hawley distributors sells 165mm (about 6 1/2") and 175mm (about 7"), but for shorter you might need to find a juvie bike to strip at your local co-op. Little bikes generally have shorter crankarms.
https://www.hawleyusa.com/Catalog/Se...cat=5637146731