Well Tom I guess we each have our preferences. I think one needs to look back and realize the Dynaco is dated and that the driver boards have served their time. As for the heat causing the components to degrade we could both argue that. Age would enter into the picture as being a prime factor. Unfortunately components don't have a life of 100 years or my Atwater Kent radio would still be like new.
If you would like to go into this deeper I would be more than happy to wire up my Blackburn board and take some temperature measurements for you. I believe you will find that the heat that you seem to be worried about isn't going to be causing near the problems that you fear.