The RF boards of the Maratrac and the similar M-400 are basically the same as a Maxtrac or Radius.
So, the "modification" is pretty much the same.
Been a while since I did a bunch of those, but the steps are pretty much:
If your radio won't accept the programming of the freqs, hack the band limits in the RSS.
You might be able to get the programming to work by entering the freqs digits with the "shift key" method.
Once you have programmed to freqs in the range you want, measure the steering line voltages ( stenciled SL on the RF board ) You want the steering line voltage between 2 volts and 8 volts for the range of freqs you want. I can't remember for sure, but I think 2 volts at your lowest freq, and 8 is going to be your highest.
One VCO is RX and one is TX, set the SL for both. Meaning, adjust one of them during RX, the other while TX'ing. If you turn one while RX and and the SL doesn't change, you probably are trying to adjust the TX. Change and try the other coil.
You will likely find that the radio will transmit WAY too much power below 146.
Look at Batlabs or Repeater-Builder for "manual TX power mod" for a way to put a POT in to adjust the drive of the RF board.
I found most of the VHF Maratracs will try to put out maximum power when running out side of the designed band. Like 180 watts or so if your power supply will handle that much current.
But, they won't do it for long.
Batlabs and Repeater-Builder have lots of info on the Maxtrac. Just treat your Maratrac the same.