First you gotta angle those wood screws 45o to grab some good wood, then you quickly pound em in, while not puncturing the driver you just put in. Worry about the big gap later.
I've had to make this decision too a while ago working on early Sony's. C631 looks to be high gain, perhaps C1845 here. The only issue there might be that Ic is only .05a vs .1 Watch out for that.
C632a & C634a looks to be more of a general purpose spec-wise, C1815 should be ok.
i bypassed the filter boards on mine. That little amp/pre switch on the back either needs to be replaced or disassembled and cleaned, mine are still giving me grief after failing to do so. I need to pull and measure that slide switch for replacement unless someone else has a part number on mouser.