As far as you do this for yourself - you can do it almost freely. The manual has all the info about schematic and parts, but layout (if you don't use the original PCB) is yours. And you'll have only limited support if something is wrong.
I use even some future modifications, change schematis, use different parts...
...its good to know that the online manual is complete and has all the information required...I think its worth building, its a well-regarded circuit.
...I am already getting parts together..., and it does all 'add-up'...
...
my own idea/plan : ...I am planning on making 'block' sections on perf-boards, each covered with a metal shielded cover and shielded wire connecting them -
sunk into earth - contained in a shielded case..., to ensure zero hum/interference etc...
...although I am rather new to tubes, from what I have read about them being prone to interference; and with common sense..., I think this will work well...
