Wow this has been onging, huh?!
You need to reflow every single solder joint. I suggest getting some flux so you're not just piling on more solder. Make the iron hotter next time if you can.
Here I am. Wondering why there's only 3 spots with no signal

Orange = red I guess.
You don't have to probe the entire board. Just where the guitar signal travels. Check for guitar signal on the middle pin (base "B") of each transistor. Where it disappears is approximately where the problems are.
The transistors are 2N2222A, correct?
Forgive any ignorance. There's a lot here.