That looks good Mark. Where'd you get the PC board?
There is at least 3cm between the tubes and the speaker mag so I am not too worried about it. There will be less than 1CM between the tubes and the wood back panel. Should be OK.
As far as the speaker goes I may put in a Fane AXA 12 AlNiCo and I am not sure about the clearance there. I will have to see.
Cool build, one thing I have noticed over the years, some of the old Gibson amps were built around the speaker. So close if the speaker is different, or a different brand tube were used, it would not fit,or would hit something. Transformers too, the OT or choke were sometimes inside the chassis.
Just no room on top for them.