Dave's right, something doesn't look right with that stopper. The tank at first glance looks like a Dubro tank, but it you look at the photo closely, there is a fuel line nipple molded in just above the bung and the the flange on the bung hole has whas looks like an outside ring to seal something. Also, the rubber bung has a huge lip at the edge of the tank. Different than any tank setup I've seen.

To get the real answer on the tank, how about removing it and removing the bung and fuel pickups and taking some photos of them and post them. Then we can advise a bit better. Garland is correct that the bung will not go through the firewall and it would be best to plug that hole and and then drill for just the brass fuel lines to go through the firewall.

Don