Were there not 318-4V enignes from about 1968 on up? I know I have seen at least one cast iron one (that weighed more than the rest of the engine, possibly), and that could have been adapted to work on a TQ with an adapter plate. People normally use a thick carb gasket anyway, so the thick carb gasket may be replaced by an adapter plate, I would think.
Just FYI, my 1980 Cordoba Crown, and my 1981 Mirada CMX both have TQs on their 318s. The 318-4Vs were only available in Canada, California, and High Altitude cars. If people are sure that the 318s during 1980/1981 had small ports (=NOT 360), then those would be possibilities. Cars are in storage, no where near me, so I can't help with P/Ns.