Actually, from my understanding it has nothing to do with A/C. The main difference between Automatic and manual transmission, is the fact that the snorkel on the air cleaner assy, has the vacuum valve on it, and the manual transmission doesn't. At first, yours seems to have this vacuum valve on the snorkle so it should fit for an automatic transmission. Is it the reason why you did not install it on your 4 speed SS ?
Someone can confirm what I'm saying please ?
For the top plate, I don'T care about the rust, because I'll have it re-chromed locally here. As long as it's in good shape, without any dent, puck, or curve on it.