Gorgeous bike. AMF Roadmaster moved from Arkansas to Illonois in 62, so it is before then, the seatpost has a clamp, I believe the late 50's didn't have that, they had a seatpost that tightened like a handlebar post. The sprocket looks like their later version, so I'd guess 60-62. There may be batteries in the tank that may shed some light on the year also. If you're lucky enough to find a roll of cash in there, check the dates on the bills.