Deep cover is used for the two-stage type power valve.

That's an excellent idea, though maybe a 1", didn't pretty much everything have a 1/2" spacer already?

Replace the two-stage power valve with a single stage, 6.5" and swap the old cover over to the new one. Two stage power valves, the idea was, that very heavy loads like when towing, maybe some fuel could be saved. Maybe. I wouldn't bother with it.

Well I'd expect a Holley power valve to fit, no guarantees though. Try the one that's in the other carburetor, since you're swapping the cover over too. 6.5" is probably the most common or generic power valve size and should work OK for now at least. The number may/should be stamped on it.

What is netting? Maybe a typo? Anyhoo a 6.5" PV should be fine for a stock engine that pulls good manifold vacuum, this is why a 6.5 is the # included in all the rebuild kits and many carburetors. You are right, it is important to select a # that isn't too high for the application and altitude, that it isn't opening at low load cruise or it will suck gas like crazy. That's why it's called "economizer" too. A mechanic's vacuum gauge is VERY useful to determine this, then there's no guessing. Here's what Holley sez:

"The number stamped on a power valve, such as 65, indicates the manifold vacuum below which the power valve is operational. In this case, all manifold vacuums below 6.5” Hg, the power valve is operating. Generally a 65 power valve is sufficient for most high performance applications that have a manifold vacuum of 12” Hg or higher. However, some problems can result with radically cammed machines equipped with automatic transmissions. These vehicles often “idle” at 2000 rpm, approx. 6.0” Hg. At this point the main nozzles are starting to feed and richen the mixture (supplied by the power valve) and the engine will probably “load up”. To correct this problem, install a 45 or 35 power valve. If the engine has a manifold vacuum of 12” Hg or less, a good way to determine power valve size is take the manifold vacuum at idle and divide that number by two. The answer is the power valve size. This will provide idling and proper fuel flow under wide open throttle conditions when manifold vacuums seldom rise above 1” Hg."