I used this setup for several years in my -4. Always seemed to work OK. The Icom Nav/Com antenna feed went to a CS10 power amplifier (check *** & others), which then put the boosted signal out to the external belly mounted antenna.
The Icom required a headset adaptor with push to talk switch, which I velcro'd to the stick.
Three or four years ago, I installed an SL60 GPS/COM, but the Icom still rides along as backup with a "rubber ducky" antenna and the headset adapter within reach in the map box between my knees.
Good luck with it,
Mel Barlow.
N114RV, 1040+ hrs and still smilin