The second generation was 1972 - 1979. Before the HX, you are right, there was not a plate. I cannot find a good DIY, but from what I have read, you remove this:
and spray everywhere with carb\brake cleaner, etc. Some people put grease on a drill bit and tap out those plugs, inserting plugs for future convenience.
Hopefully someone more knowledgeable will be able to provide more help!