I fixed it!! 
I saw that the vias around C35 didn't look so great, and started tracing to see where they went. I found one which tested ok to the bottom of the board, but for some reason wasn't connected to its trace on the top of the board.
Turns out this is the main 12.5 MHz clock input to the SYNC pin of the MC88920 clock driver (down near the speaker connector)!
I ended up running a wire from the bottom of the board (the easiest place to tap this signal) to pin 7 of the MC88920, and it works!
It even has a 32MB SIMM
Anyone with a Quadra 605 / LC 475 that's not powering up even with new caps and a good battery should check that pin of the MC88920, it needs to have a square wave on it.
I saw that the vias around C35 didn't look so great, and started tracing to see where they went. I found one which tested ok to the bottom of the board, but for some reason wasn't connected to its trace on the top of the board.
Turns out this is the main 12.5 MHz clock input to the SYNC pin of the MC88920 clock driver (down near the speaker connector)!
I ended up running a wire from the bottom of the board (the easiest place to tap this signal) to pin 7 of the MC88920, and it works!
It even has a 32MB SIMM
Anyone with a Quadra 605 / LC 475 that's not powering up even with new caps and a good battery should check that pin of the MC88920, it needs to have a square wave on it.