Here's the SDB upgrade link: http://www.pinwiki.com/wiki/index.php?title=Bally/Stern#Solenoid_Driver_Upgrades
Normally, I buy the Bally solenoid rebuild kit from Ed @ Great Plaines Electronics, but he's out of stock. However, you can still use his values for reference ordering from Mouser or Newark (o whomever is your electronics go-to).
Ed also normally has all the connectors & headers to repair/bulletproof the boards.
And actually, it's a "flipper enable" relay, that is held closed by Q15 (also get from Ed @ GPE). Sometimes you can steal an unused transistor elsewhere on the board. There's a great matrix chart that shows which unused trans you could move: http://www.pinwiki.com/wiki/index.php?title=Transistor_Mapping_for_Bally_Games
Beyond voltages found in the manuals (and on the various PinWiki pages... that's all you generally need on these Bally's.
Also, there are several aftermarket makers of brand new & improved Bally board sets. I don't recommend trying to retrofit a generic power supply to provide voltages.
And I've only replaced the Bally rectifier of this series, when the original was truly toasted.
If you're halfway decent with a soldering iron (and solder sucker/desolder gun/tool)... these are fairly easy boards to repair. IMO
And... if you've got any display issues: http://stevekulpa.net/pinball/bally_disp6r.htm