There's nothing to mount a turn signal switch to on the right side of the column. The originals attach with a single nut to the plastic shroud instead of to a bracket on the column, just like a regular toggle switch.

I've installed the switch IPD sells (mounts the same way), and I'm not impressed with its sturdiness. I had it fall apart several times trying to make it fit, which is just barely possible. The one I did does seem to be working fine after a year, though.

Using the pullback feature on the turn signal switch works great, but you've already got the headlight dimmer wired to that.

What I did on our own 122 is use an illuminated rocker in a bracket below the dash, held on with the same screws that anchor the bottom of the heater controls. No new holes needed, indicator light is built in, and to me it falls readily to hand.