Hey guys,I need to know the size of the screws used to attach the fuel filler to the rear panel. thanks..

I believe them to be #8X3/8 or 1/2" self-tapping sheet metal screws because of having a 5/16" hex head.

You could get by using the self-tapping screws used in sheet metal duct work. These have the same shape head as original, IMO.