Well, you just bought a rare bow. A real collector's item
I have one of those. Great shooter, but it is not a true Jack Howard. It is a Damon Howatt Hunter finished by Jack Howard with his logos. While it does not have Jacks limb design, there is nothing "slouch" about a Howatt Hunter. Jack only did about 50 of those. Several of his customers were pressuring him to come out with a 62" model. His standard was 66". Instead of retooling for a 62". he bought 50 unfinished Howat Hunters and marketed them as the "Jack Howard Hunter"
Another suggestion is to drill the holes a bit wider to about 21/64's and install brass bushings. This can be done to look like a factory installation,
When I bought my first JET from Jack, I had him install a set of these on the riser. I mounted a Kwickee Kwiver on it. He also mounted a compass on it for me. This was something he never did and it took some talking to get him to do it.
You can get the proper bushings from 3 Rivers Archery.
I have picked up a couple of bows drilled for sights on the back or front of the riser and done this to camo the drilled holes.
The down side is that the holes were drilled to accomodate a particular sight and there was no "standard" back then, Each model sight was different. Thoes drilled on the side of the riser wer usually the standsrd for hanging a bow quiver.
If you fill the holes, you will still be able to tell they were there. The bushings make it look like they were supposed to be there.
My Jack Howard Hunter came with a "Heart Shot" site. That is what Jack used and sold, Many of his bows were ordered with the sight so he mounted them for the customer. I left mine on the bow.
Jack was a master bow hunter and was one that pioneered the use of sights. With four pins, he had his personal bow calibrated out to 80 yds. and took many big game at that distance.
He also pioneered "bivy" hunting. He would take to the wild with a pack and bivy shelter and live amoung his quarry for a week. He was known to single out one Mulie or Elk, pattern it, and hunt it alone, passing on other game in his quest for the one he was hunting.
One such adventure is detailed here:
http://tradgang.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=4;t=000108