The flat bolt may be right for his carbine. Remember that what ever was on hand was used till it ran out. Rock-Ola did use the type 3 round bolt in the 6 million range but it very well could have been in mixed use with the type 2 till all of the type 2 bolts were used up.
True, either way though he should leave the rifle alone and not try and correct it. It's a very nice carbine just the way it is.