With some games, the artwork just adds to the experience; with others the game makes no sense without it. Safari is one of those games. The cage is a "safe zone" where you can shoot animals but not be killed by them, and there's a tree in the middle you can't shoot through.
Using the grainy black & white photo on the flyer as a guide, I pieced together a backdrop from top photos of the Taito version of the machine (one shows the left side up to the tree in the center, the shows the right side just past the tree). I had to get a little creative filling in the lower portion but it seems to be just grass anyway. I drew a cage to match the one in the photo which seems to have been a sticker applied to the screen/mirror. The bezel is from Mr. Do's WIP site. I cleaned it up the scratches a bit but it would look nicer if it was vectorized. I have no idea if Gremlin used the same backdrop as Taito but it seems to match the flyer.