Well, I finally got a result I could live with in applying satin finish Minwax Spar Urethane. I left the original ink lettering and blended it in as well as possible.
The first two coats went on like corn syrup and dried badly, leaving drips and runs. I sanded them back and tried a 60/40 mix with mineral spirits and applied it with old, well laundered (and lint free) cotton. Each application went on thin and I worked out a few runs each time with 400 grit and OOOO steel wool. Last three coats were 80/20 thinned and applied with a foam brush.
Came out pretty good. I radiused the shelf (it was flat) and you can see one spot just above the thumb groove where I didn't blend in with the old finish very well.
I wiped the limbs with linseed oil and it darkened the minor scratches vey well.
You can see the original ridge line of the flat shelf in the below image.
Sorry, no before images - but picture a 1969 bow that had been used and chipped and refinished with a glossy finish heavy on brush strokes.