Does anyone know if it's possible to hook up a GAZ4 scoreboard with FinishLynx system so that the start impluse from the starters gun triggers the scoreboard?

Yes this is possible and works quite well. You will need to use a c-box to receive the start impulse via the XLR connector, a photocell will need to be connected to the c-box to recieve the finish and stop the board. Camera will need to be connected with a DB15 cable to the c-box and display board to the c-box with a DB9. Settings on the lynx software scoreboard tab will also need to be configured. Read your manual and bench test until you have perfected your setup.