Is it rare Poly 318?

The "Poly" "A" small block engine came is 3 sizes, 277, 301 and 318. They were built with very strong parts. They also use some "LA" parts. Valve springs, yiming chain, crank etc....

Some performance parts are out there for this engine. Used intakes in 4bbl. and dual 4bbl. can be found in steel factory offerings and aluminum from Offenhauser and Weiand.

New cams can be purchased from Racer Brown. He'll also do a custom cam if you want.
They can be hooked up to modern OD tranny's though some cranks are not ready for it as older versions have different diamentions for the older tranny's. It'll ethier take a crank swap or machine work to get it done.

Mopar muscle had a write up by Gary Polvich who stroked one to 400 cubes and made over 400 HP.
Currently, I knw a few Aussie's working on a new intake manifold fore the engine. A RPM style intake is being developed.