We ran mostly blown motors so there were only a few brands of manifolds available.
There are spacers for the intake available from the hemi site above. I think they are 1/2 inch thick and allow a 354 manifold to be used on the 392. It's been along time but I made a bunch of these in school that we passed around the dragster guys in the 60's and 70's. I can't remember what it was about the heads but we used either version with or without spacers as required. Make sure you get them sealed up good. I think the hemi site has some identification numbers available. Most everything else fits. If you have the 300 heads you should have adjustable rocker arms. Very rare even in the old days. they are much easier to adjust than adjustable push rods.