My question is, if you take a set of limbs made for a 64" bow that was 60# at 28" and put them on a shorter riser and made it a 62" bow what would the draw weight be?

That is only 2" shorter; new bow will be 61#@28 (using the old Bear TD formula)

Bjorn:  All of my Bear limbs show a 2# or sometimes 3# difference between riser lengths. Those risers are 4 inches different from A to B to C though, not 2, so your number is probably correct.  However, when I had several Bighorn T/D recurves with different length risers, I also found about a 2# difference when going up or down two inches in riser length.  For what it's worth.  Regardless, it's not a big difference.