Congrats on the amp and nice work using that NOS rectifier tube. The idea is to keep the heater (6.3v) twisted pair away from the rest of the circuit, especially the signal path. So, I would fix that….
Follow DH’s recommended grounding scheme is important, not to say that it can’t be done differently, but unless you understand the how the grounds affect noise in the circuit, sticking with DH’s design is safe. The ground plate is not mandatory, but it works well for the Two Stoke (and Fender). You can use a buss bar too, as long as you avoid ground loops.
Use you meter to confirm you have good grounds where they are suppose to be. The filter caps for the power stage should not ground to the preamp side. Is you amp passing a signal? or just noise and hum?

Since you specs you own parts (I did that too), I’ assuming you are up for discovering more about tube amp circuit design…check out: http://www.valvewizard.co.uk/
Don’t give up, you are close…