Yes, I unplugged the big connector for the glow plug wires at the relay and measured resistance there. Also confirmed the relay was putting out 12+ volts to each of the 5 pins.

If there is something wrong with the injectors, how would I verify or fix that?

Since switching to the bottle of fresh fuel as my fuel tank, it is sputtering much more. For the first second or two of cranking, it feels like it's firing on at least 1 cylinder. And then I smell a little exhaust come out.

I'll check the filter, I guess a rat's nest could stop air from going in, haha!

If I need to take injectors out, what tools and new parts will I need to put some good used injectors in?