Have such a setup on my RT. Autocom Pro 7 system connected to a Cobra 38WXST CB and Kenwood TK3101 FRS/GMRS radio. I use the Autocom PTT and a switch box to select the transceiver I want to use. Also have a Kenwood TM-D700A ham radio for APRS and repeater calls. Same switch is used to select between them.
Biggest challenge is to isolate ground loops and to understand how the radios support PTT.
You didn't specify what CB and FRS radios you plan to use and whether Autocom supports either via special cables. Most likely it will involve more than just building a 5-pin to 7-pin cable.
Herman van Beek
2M/70cm/APRS - K5HVB(-10 when mobile)
FRS/GMRS - WQGD850
2005 F650CSA (Silver)
2005 R1200RT (Silver)