I was thinking charcoal gray or dark brown for realism and contrast as a backer paper.
The pattern is intended for a regular frame, as shown by the straight
line of the cutting along the right hand border, the antelope are even cut off as it would from a photo. So I would suggest a regular frame and perhaps cut off some of the margin along the right side to put it in balance. I don't think I'd get too carried away with the torch and "antiquing" it any thing like that you should do a test run on some of the scrap to see what the effect will be.
Great job of cutting and a very nice Bull!
Gabby