Those pictures really show all sides of the wiring. I'm afraid I'm getting to the point of diminishing returns this way though, without having my hands on the chassis to be able to make tests and check continuities, etc. I think now the best thing would be to inject signal into the 6K7 IF stages to see if they carry over through the detector and audio stages, and to see if the 6A8 oscillator/mixer (also called converter) is working. Any wiring mistakes could throw this off greatly but you did say it worked somewhat in the beginning. Is there anyone local with a signal generator and signal tracer that could help? Going that way could localize any trouble a lot more quickly.
I found a good source on line that discusses troubleshooting superhets and they use as guinea pigs a 6A8 converter and a 6K7 I.F. stage (of which you have two) with diagrams and items to check.
http://www.radioremembered.org/superhet.htm
They show a tube in an R.F. amplifier stage before the 6A8 but you don't have an R.F. stage so that could be ignored. The detector and first audio is a 6SQ7 I believe but that's the same as a 6Q7 without the top cap and all electrodes brought out to the base pins. The audio output tubes seem to be OK in your case so just the 6A8, 6K7's, and 6Q7 need inspection for now.
I'd start checking the 6K7 diagram against your radio; they may not be exactly the same in components but close. Then do some of the checks. The voltages you'd get are going to be less than in the article because they're using a transformer set that ups the voltage and you're using line voltage as a source.