Peltor Comtacs are made so that they can fit under the ACH/MICH. They do not need to be modified to fit a helmet, adjust the pads inside your ACH/MICH so that they fit comfortably.
No, these do not come with the gel cushions, they can be ordered separately here: https://www.opticsplanet.com/peltor-aviation-parts-ac-camelback-gel-sealing-rings-hy80.html
No. This model does not have leads for connecting to a 2-way radio, and it cannot be modified for use with a 2-way radio. This model features the NIB (Natural Interaction Behavior) for Peer-to-Peer Headset Communication, which allows up to 4 team members to speak simultaneously within 30 feet of each other and 60 additional people can listen.