Stock-ish 383 Build

...with a dome...

here's some more info on casting numbers:

Mopar Casting Numbers - MyMopar.com - Mopar Part Numners

it says your 213 castings are from a later model motor home? My guess would be sometime during the life of that engine the heads were swapped, as the factory castings, even for a 2bbl Polara, should've been 906s or possibly 346s

tellin' ya man, you really need to look up some of IQ's builds and not get hung up on SCR, except to choose a suitable cam and match ICL to make the most of the SCR you do have.