I'm sure you'll get a lot of input from real experts today, but I will give you a few high level comments.? Check out w8ji.com and read everything there about amplifiers.? Tom designed many tube amps for Ameritron and others over the years and is a good source of practical knowledge.? Also, read everything you can find by VE7RF.? He has written a lot on eHam amplifiers forum and elsewhere on building large amplifiers.? The older ARRL handbooks are a good source of amplifier circuits and info.? I have a 2004 Handbook with some interesting amplifier circuits.? On Facebook, look for the group "Amplifier Building and Homebrewing" - lots of good info there and you can converse with W8JI on difficult amplifier questions.??
Seems to me that just a single GU5B will deliver the legal limit easily.? I see that someone in Europe is selling sockets for that tube although they are quite expensive.? One area of concern is always the plate choke and it's a challenge to obtain one or build one that works properly on all the bands without resonances that can destroy them.? W8JI has good info on that.? You probably know that you won't be able to obtain tune and load capacitors at the needed voltage level and the capacitance range shown in your diagram.? Typically fixed capacitors are switched in for the lower band or two.? A good example of a fairly modern tube amp with these considerations covered can be found at AlphaRFSystems.com.? Here's a link to the Alpha 99 schematic:?.? That's a tetrode amp, but the site includes others info on their earlier triode amps such as the Alpha 86 and Alpha 89.??
To the questions "Am I mad?".? Maybe not, but you will be by the time the project is finished!
Floyd - K8AC