If you want my honest opinion, I think that bow is done. Sand it and shoot it in and it should be close to 50# at 28". 1 5/8" set is fine, nothing wrong with that, but if you really do want to remove some set, you can try heat treating the belly.
I've never made a sinewed back bow, so someone correct me if I'm wrong, but if you add sinew it will take some set out but will also raise the weight of the bow.
Oh, and congratulations on your bow!