I consider myself a decent Tech and it was one of the most difficult things I have ever done in my 40 years on earth.
One of the preamps had about a dozen mistakes when I put it together.
I went back through it, over and over until each one was corrected and eventually I checked it on my test gear and got good performance.
This isn't a job for a parts swapper, nor is it the job for a guy who replaces an electrolytic or 2 and declares "good as new"
This is an extremely involved multi year process involving sourcing parts from multiple vendors, careful documentation and tear down and meticulous reassembly.
Simple: extremely.
Easy: No, other end of the scale...
Worth the effort: 112%

Look at em.
They're absolutely gorgeous, sound great, and have made it 70 years without becoming obsolete!
One of the preamps had about a dozen mistakes when I put it together.
I went back through it, over and over until each one was corrected and eventually I checked it on my test gear and got good performance.
This isn't a job for a parts swapper, nor is it the job for a guy who replaces an electrolytic or 2 and declares "good as new"
This is an extremely involved multi year process involving sourcing parts from multiple vendors, careful documentation and tear down and meticulous reassembly.
Simple: extremely.
Easy: No, other end of the scale...
Worth the effort: 112%

Look at em.
They're absolutely gorgeous, sound great, and have made it 70 years without becoming obsolete!