1. Your 4 missing chips are the speech ROM's. So yeah, you won't get any speech with those missing. Any of the ROM suppliers should be able to take care of them for you. They are 2532's on an original System 7 speech board, though System 9 speech boards have jumpers for using 2732's or 2532's. Once you get those, don't be surprised if you have to do additional work. The ribbon cable is the most common failure on the speech board due to the sharp bends, followed by the op-amp's, and once in a while the decoder chip.

2. For the GI on Black Knight (and all other System 7-9 games), LED's are essentially mandatory. At the very least convert the backglass to LED or you will continue to have long-term issues. The reason for this, and also for the hack on your power supply, is that the GI lights pull about 40% more amperage than the original power input connector is rated for. Even the 9-pin molex connectors burn up pretty regularly. There is actually a separate fuse for the backbox GI on the back-side of the lamp board, most people never even notice it. I'd check to see if that's even present. Otherwise you'll have to trace out a wiring issue. All the GI runs back to that single connector on the power supply and if the relay is working then it's got to be a wiring issue.