One of the things I'm not seeing that may be the cause of your hum, is lack of a filament ground reference. In the original Dynaco design they grounded the center tap of the filament transformer(s) via .02 capacitors. I don't think you have centertaps, so you need to create them on each side by connecting 100 ohm resistors (2 watt) from each side to ground. I'd do it at the EL-34 socket where you have some room. Take a look at the ST-35 manual, page 13 and look at R40 and R41, you need that on each side. I think that might be your problem.
... tom