Bore spacing on the three Hemi families is different. AND, the 318 Poly is different from all three Hemi bore spacings. www.hothemiheads has many answers as does Wilcap and TR Waters.

Chrysler Corp started making Poly motors to give themselves a less expensive engine. The Poly heads from a 318 Poly won't work on any of them. The Chrysler Poly heads bolt right up to a Firepower Hemi block. I believe they used the same intake manifold as well, Hemi to Poly. BUT there is a fly in the soup!

The 392 deck is 1/2 inch taller and in order to keep intakes swappable Chrysler made the 392 heads wider so the intakes would bolt right up.
There wasn't a Poly 392 and so all the heads were sized for the lower deck height. If the mythical racer used an intake from either 392 Hemi or other Chrysler Spitfire engine he'd have to use spacers for it to work. The aftermarket had no such animal as an intake for a 392 with Poly heads. SO, the story is a myth or the buy was really handy with tools and machinery to fabricate his own spacers.

Firepower bore spacing - 4.5625"
A engine (318 Poly) bore spacing - 4.46"

They do not interchange either.

I think the story is a myth generated by some alcohol-fueled bench racing.

R.