I'm using one of Sheldon's 6AU6 boards in an ST-70 I built from reproducion parts on the internet. I got it from Triode Electornics. It works very nicely, but I'd be lying if I said it was better than the stock set up. It was designed to use the same circuit with more available tubes. I would have bought a repro 7199 board if the tubes were not so over priced or unavailable new.
There is a 6GH8 board available that is the same as a stock board, just with rewired pin locations. It would work similar to the ST-70 Series II which also used the 6GH8. According to Dynaco, the 6GH8 was comparable in quality to the 7199. Subjective at best I'd say.
Or a 6GH8 converter is available for the original or replacement boards. There are many other boards that depart from the original topology for many reasons with varying degrees of success.
The point is there are many choices from stock, to modified, to flat out major upgrades (like the VTA board).
My choice was to try using the original circuit with other tubes and save some money for the transformers and chassis and other parts while staying electrically stock. Had I known about the 6GH8 board, I may have tried that instead.