paint code 557

[71 Chevy Cheyenne]

I have read a lot of your on paint code 557 but am still unclear on a couple issues with my truck. Hope someone can help?
I have a 1971 Cheyenne code 557
Truck is currently white on top and stripe around the middle with rest in dark olive 506. The white in the middle is clearly painted over dark olive 506 and the white on top also appears to be painted over dark olive 506. The interior (dash steering column rear sheet metal) is all medium olive 504 ( it all has the appearance of being original color) with the exception to the inside of the doors that are dark olive 506 (these are clearly repainted).
I see that my roof should be medium olive 504 but need help on the middle part...
1. My truck has both moldings so should my middle part (between the moldings) be dark or medium olive? I have seen both and even some with both moldings and still dark olive in the middle (but have only seen that combo on a 72 not a 71).
2. Does it make since that my interior is medium olive, with dark olive doors, and a dark green bench seat and head liner? Do I need to repaint the interior of the doors to medium olive 504?
3. My urgent issue is I am repainting the engine side of the firewall in the next day or two and do not know which olive to use. The engine side of firewall and engine side of the passengers finder are black (repainted over an unknown color). the engine side the drivers fender is medium olive??? Maybe that fender has been replaced with a used fender??? What color do I paint the firewall (looking to be original)?

thanks for any assistance you can provide...