I recently assembled my first solder-on KBC-PS2 adaptor. With the VIA KBC's at only about $2/each, I felt OK with snipping off all their pins. I'm not sure if I would do this with the more expensive KBC's. I would only do the solder-on if the KBC is behind the ISA slots, as shown here:

Due to the height of the 14-SOIC inverter package, this is as close to the PCB as achievable:

The KBC clears the ISA drop-down PCB by about 1.2 mm. I am using 0.6 mm PCB's. If using standard 1.6 mm PCB's, clearance would drop to about 0.2 mm, or just hitting:

I needed to run the inline mouse header again, otherwise the header would be in the way of the ISA card:

On some motherboards, the KBC socket is flipped 180 degrees. This is normally fine, unless you are running an ISA card that has the wrap around support on the slot bracket itself. Luckily, very few slot brackets have this wrap around.