Steve -
The Hoyt ProCustom with that serial number (2PC607) was most likely made in late 1963 (maybe October). I think that this particular bow was made by Hoyt, not Howatt (based on the 2PC bows that I have seen), although I have seen a Hoyt bow that I thought looked like it was made by Howatt, myself. Pictures would help, here.
Those series 2 ProCustoms are beautiful bows. I have never seen one that was 55#, though. And, the 64" is also unusual - most that I have seen were 68". I would like to see photos of the bow, if you can post them or email them to me.
Ray