[FWB]

all the stallions have this problem, the vent in the cap is not large enough or in most cases isn't there at all. some of the cars with the fuel cell(fiberglass) seep fumes thru the cell. if the cell you are using is from 1981 i would think about changing it for safety reasons. i had a stainless steel tank made up for my stallion. the fuel filler casting that the fuel hose connects to can be drilled and tapped just below the body for a fitting to put a good sized vent in. you mentioned the new fuel cell is vented thru the cap, isn't that in the trunk? has the original fuel; filler been relocated?