Heads and cams hold the Poly back. Intakes are avilable but as said, a bit crazy in price.
A new intake from Chrysler Power is available. At $600 (or so) that is really expensive! But a low run (basically custom) intake is allways going to be that way. And for any antique engine. The Poly was not what I'd call popular ether. That's 3 strikes on it. The only benifit to it is that it shares parts with the LA. While a real plus, I don't consider it a great one.

The CNC heads are nice. The rocker issue isn't sorted out just yet. Once the rockers are fitted, that guy could brake 500HP with the right cam.

The poly uses the same cam length as an LA. It's IEIEIEIE prove to be the problem. I myself have not looked into this.

TTI makes Poly headers and exhaust to hook up to it for many makes and models.

Truly, this "A" engine is one that you want to build. Other engines are cheaper.