Hi Mose and Welcome --
The PCB in your ST70 was made and marketed by Purist Audio Design in Lake Jackson Texas (about 40 miles south of Houston, Texas). It was one of the Replacement Boards that Roy Mottram reviewed for Glass Audio Magazine back in the early 1990s.
The version of the board that I bought in the early 90s used 12AX7s tubes and gave you the ability to indiviually set bias on the 4 output tubes, so matched pairs of tubes were not needed. 12BH7s could be used, but dropped the output level because of the reduced gain that the tube provides as compared to a 12AX7. Bob mentioned Sal in his answer to you and Sal had a version of your PAD70 that he repaired for a customer because it had very low output and was using 12BH7s. I know, because I sent Sal a copy of the PAD70 documents that I had and I believe that he replaced the driver tubes with 12AX7s and got the output level up.
As to what else was done to your ST70 -- obviously, the Quad Cap was replaced by under chassis Capacitors and because of how those caps are placed, the Choke was moved over to the far left from the far right. The missing Dynaco Bias Pots were removed when the PAD70 board was mounted and has that functionality. The stock Selenium Rectifier was also removed because the Diode that normally replaces it is also on the PAD70 board.
I hope this is what you were looking for and helps. If you need more info just ask.