That weird operation with corrupted SRAM is possible, with all games prior to Escape From the Lost World, they aren't validating the SRAM contents during startup. All games from Escape From the Lost World to Atlantis will reset the SRAM automatically if the game detects that SRAM contents are corrupted. This is also indicated by the units digit increasing by 1 when the game shows the "Beat for 3 Replays". For instance, if the HSTD is 3.000.000, the game will display that as 3.000.001 if the game had to reset SRAM at some point. In these later 6803 games there's unusual feature: to reset the settings to factory ones on startup, hold both left and right coin switches while you turn the game on. The SRAM seems to be in the socket from the factory. Installing the NVRAM should be easy, if you happen to have compatible memory chip - this will allow you to remove the battery from the board, since it won't be needed with NVRAM installed.

Nice pickup! I saw the pinside listing the other day, glad it went to someone who's going to clean it up and make it look nice. I picked up an Eight Ball Champ a year ago and I had to do a ton of board work on mine. But really happy to have it, it's a fun game, and a good tournament game as well. Looking forward to seeing your progress!