Looks great! I assume you'll be building a Marshall type of cabinet. Be aware that your OT is sitting close to the edge of the chassis and be sure it will not conflict with your cabinet.
My current project is a #124 low plates, non HRM with 2x 6L6. I see different versions of the screen grid resistors: 470 Ohm or 1 k. What do you people recommend and what is the impact of either?
Also, what would be the best feedback resistor for a 50 W. version?