A 305 (aka 5.0L) is a GM SBC.
A 302 (also a 5.0L) is a Ford 335 series engine, such as the Windsor.
Your thread title says Small Block Chevy Heads, so I'll assume that you have a SBC engine.
There are no typical press-fit casting core plugs in the SBC cylinder heads.
SBC cylinder heads are easily identifiable by the exhaust ports being siamese at the center.
Valves will be:
Exh/Int... Int/Exh... Exh/Int... Int/Exh.
The above is a heavy casting. Light castings usually have the
full scallops at the low side.
If you have casting core plugs in these heads, they are likely Ford heads, similar to these.
(you can see one core plug in this image)
The exhaust ports are evenly seperated in the Ford cylinder heads.
Valves will be:
Exh/Int.... Exh/Int....Exh/Int....Exh/Int running down the Port side.
From front to rear, this will oposite for Stbd side.
NOTE: There are several combustion chamber volumes for the SBC cylinder heads, as per the different castings.
I agree with Kghost....... Do Not replace with un-like chamber volumes, or you'll change the C/R.
You'll want to find your existing casting numbers, and search those numbers.
If you use a good casting number data chart, the chamber volume should be listed.
FYI:
Engine rotation direction is always viewed as though from the flywheel end, not from the front end.
CCW rotation is an industry standard LH rotation, same as car/truck as shown here.
CW is Reverse RH rotation.
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