Going by memory here so...
IIRC, the ('uniden boarded') 148 and 2000 are dual-conversion on AM only, and may contain the MB8719 or MB8734 chips. The chips are essentially the same with the 8719 having an "n+64" pin not present in the 8734. The loop mixing crystal is of different freq. depending on which chip is in the radio for proper 'legal 40' coverage depending on what value 'n' is in the PLL loop, determined by the PLL chip that is present.
IIRC, the ('uniden boarded') 146 and 142 are single-conversion chassis, most probably containing the 8734. Replace chip with 8719 and change loop mixing crystal to 11.25 MHz IIRC. Then you could use the (n+64) pin of the 8719 to get channels above 40, to a max of 28.045.
That should do it.
_____
Buttfuzz in the Mobile</p>