Right tools for the job...
I have not actually worked on many /6s but "in general" do not be afraid to modify wrenches. Go down and buy some med. priced import combo wrenches. Not the cheap chineseo, but something "in between" good name brands and the cheap stuff
You can BEND these if you are patient with, believe it or not, a propane torch. Put the wrench in the vise where you want it bent, get vise grips or other large device for leverage, or a hammer. Heat the thing in one spot, back and front. It WILL bend.
I used to have several "custom" wrenches back in the day, for changing plugs on stuff like 428 Mustangs, BB Chevelles with headers, and so on.