"Agree with the icom. Agree with at least having a T connector to the present COM antenna installed, so you get the range. "
Not sure how you were intending to do this. If you we're simply thinking of getting a BNC T piece, and plumbing the handheld in with your regular com/nav stack coax, please read the following...
Speaking as an RF Comms engineer and designer, there are a whole bunch of reasons not to do this.
The most important one is that when you transmit with either radio, you will almost certainly blow up the front end of the receiver in the other one. This will happen in a very short time (sub second).
Secondly, whether or not you've blown up at least one of your receivers, using a simple T connector will ruin the impedance matching to the antenna, and quite possibly blow up your transmitter's PA stage too. Even if it doesn't blow up your transmitter, protection circuits possibly in existence in the transmitter on the unit may well fold back output power when detecting the mismatch, limiting the effectiveness of your transmitter.
Either or both scenarios could most certainly mean a bad day at the office.
I apologise if I've misunderstood what you were suggesting, but that's how I interpreted it.
Many thanks, Howard