I use Gun-Sav’r Hunter Satin from Brownells. Blends very well with whatever finish is used by Boyd’s. This is from experience. I have done a number of rear tang mods where I reshaped the top rear of the wrist to better conform with the top of the Kidd rear tang in use. Just spray as you would any other finish. Light coats.
Quick note. Only works on the standard finish. High gloss stocks are another matter entirely. Stuff is now more than doubled in cost per can. But it does work and it’s a great finish. Very durable