73 318 will J heads work???
Maybe a 318/360 Magnum head might be a good choice for a normally-aspirated L-A 318. The Magnum heads have 60 cc combustion chambers, and small, but high-velocity intake ports, and a fast burn combustion chamber.
They might work as well as a 302 head and are easy to come by in wrecking yards; just be sure to have them tested for cracks, as I hear they do like to crack around the exhaust seat area.
I can't recall all the changes necessary to successfuly install Magnum heads on L-A engines, but if I remember correctly, you need Jeep lifters and pushrods with an oil hole in both ends, so that the upper end gets lubed.
The Crosswind "Air Gap" style (Chinese knockoff) manifold has both vertical (Magnum-style) attachment bolt holes and conventional, angled holes, and is pretty cheap.
Is that a viable option for a 318? My 360 Magnum has dished pistons for a true 9:1 compressuon ratio, but I've never seen what the 318 Magnum pistons look like. They could be flat top, for all I know.
One bonus might be the 1.6:1 rocker arm ratio that is stock with the Magnum valve train.
L-A headers work just fine with Magnum heads.
Food for thought...