That's one of the best machines ever made! He should be able to work on it and get it running. Parts are still available and guidence if you need it on the web. There are several vintage Singer Yahoo groups with knowlegable nice people. You gotta love those old Singers. I have way too many of them but I just can't resist buying them.
'Hope you both enjoy this wonderful machine. Mary
PS it threads the same as the 500 series. Manuals are readily available for free download on many Singer sites and Yahoo groups. Try Singer Slant Sewing sites. If you can't find one let me know.
Mary