A couple of comments on the valve adjustment, since you sound inexperienced. Whoever told you these are not adjustable was thinking of the newer LA engines, which cannot be adjusted, normally
Get the hot lash spec from a reliable source, such as a Chrysler dealer --make them look it up in "the book" I don't remember for sure, but I think the "real" spec for these engines was "hot"
or the old "blue" Motor's manual
I don't remember if the 318's had the "self locking" adjustments--I.E. you just turn them--or whether it had locking jam nuts with slotted screws. These last type are the most secure, BUT they are a pain in the a@@ to get right because you MUST get the jam nut tight without moving the adjustment. Take your time and be careful
When you use your feeler, I like to take two feelers--set one up for the spec lash, and the other for maybe .002" or so larger. You want to be able to get the "spec" gauge in, but NOT the .002 larger.
FIRST, though, just check your lash without changing it. You'll want a "remote starter" switch so you can bump the engine over on the starter without having someone "on the key."
Something you'll probably want to do--you really should find a good factory manual, or at least one of the old Motors manuals--something you should do is draw out a diagram of one head so that you know which valves are intake, and which are exhaust Sorry, I no longer have these books after a house fire. Actually, on your "poly" engine, that part is easy--the exhaust's are "on the bottom" of the head, and the intake's are "on the top."
Here's a couple of pages, geared to (gasp, yuk) Chivvy engines, but the same applies to the 318
http://www.classiccarauto.com/impala...t_valves.shtml
The second is a "quick" method, and WILL NOT WORK with all engines, especially ones with huge cams. I'd try the first way, then go back and see if this first one checks out, and you'll know if you can use it in the future
http://www.centuryperformance.com/valveadjustment.asp
You want to be ABSOLUTELY SURE that you get the engine bumped over so that the lash is at it's "most" when you check it. You might want to call this a "practice session" and plan on rechecking things again. I'd think twice before changing a setting --until you are sure that the adjustment is indeed wrong to start with
I used to run one head first, front to back, then go to the other side of the engine
On your valve covers, here's what I used to do:
Clean up the covers real good, and carefully glue the covers to the new gaskets with your choice of Permatex. I used to use "aircraft" something, I've forgotten. Put a LIGHT film of oil on the HEAD side of the gasket, so, if you're lucky, you can get them off again. If the covers are "straight" (not warped) they won't leak. DO NOT OVER TIGHTEN. Valve cover bolts are only a "few inch pounds" you can tighten them with a screwdriver handle like a nutdriver. That is, just light hand tight. Otherwise, you'll "dimple" the cover at the screw holes, warp them, and they leak.
Here's something to make you drool:
http://victorylibrary.com/mopar/poly-graphics.htm