Disclamer: I only play a mechanic in my garage on the weekend, and classics are my forte.
P2277- is O2 sensor stuck rich, if that is the case it would be giving a false reading and the computer would be leaning the engine out to correct a rich mix that is not really there. Causing the P2187 - system to lean at idle.
So bad o2 sensor would be causing all the lean codes. There is one before and one after the cat, not sure if you disconnect one o2 sensor connector if it will default to running off only the other. If so the could confirm this bad and which, but if one is bad its good practice to replace both.
They are a common fail part.
Hope this helps.
I will stick to my carburetor, these computers make gas, air, spark way to confusing, lol.