Having or not having a Ram Air block has nothing to do with how well the heads work to make power. The crank/pistons/rods make up what is called the "rotating assembly" and are not considered part of the block. The rotating assembly contributes to power output because the combination of bore/stroke defines the swept air volume - cubic inch displacement. The parts are installed into
the block. It can be a little confusing because the combination of engine block and rotating assembly is what is referred to as a "short block".
Likewise the cam shaft - not part of the block. The cam, lifters, pushrods, rockers, and valves collectively make up the "valve train". The heads plus valve train make up what is called the "top end" of the engine and is also the second primary determinant of power output because these parts determine peak volumetric efficiency (how much of the swept volume the engine can actually use) and also the rpm where peak VE occurs.
As already noted, RA III's are pretty much the same as any other D-port, large valve head. Do NOT try to run these with flat-top pistons on a factory spec engine even with 93 octane, let alone 91. You might as well take a hammer and knock holes in the tops of all your pistons before you even assemble the engine and save it the trouble of doing it for you.
To use them with 91 octane, you'll need pistons with at least
15 cc's of dish volume in the tops, assuming everything else is nominal.
With the 7K3's, you have the opposite problem. ASSUMING
that they are actually 96 cc's (they may have been milled, and also untouched heads can vary quite a bit from the published specs), you'll be at 8.144:1 on a factory nominal 400 bored +0.030, lower if it hasn't been bored. IF
the heads are 96 cc's and IF
they've never been milled, you could mill about .045 off them and get close to 86 cc's, which - along with zero-decking the block - would put you at 9.150:1. But before you start cutting on anything, make sure you measure everything, all the chamber volumes, piston deck clearance, head gasket compressed thickness and gasket bore size - first. Also, milling the heads that much is a one-way street. If you ever need to rebuild the engine in the future and have the heads "decked" to make sure they're flat, there won't be able to without leaving that surface too thin to use.
As far as ID'ing the heads. On any piece of Pontiac cast iron, always start with the 4 character date code FIRST - to determine the model year of the part. Then you can use the casting code to ID it correctly. (If they're model year 1969 with casting code 48, then they're both 350 heads AND RA III heads - it was the same head.)