I acquired several Icom IC-H12 radios, and some IC-H16Ts including original issue Service Manuals for them.
Here are links to some scanned documentation. The H16T service manual is widely available, but I scanned the foil pages since Icom official scans are useless there.
|Icom IC-H12 Service Manual
|Icom IC-H12 Service Manual.pdf
|Icom IC-H12 Trimming Note
|Icom IC-H12 Trimming.pdf
Several notes on adjustments
|Foil pages for the H16T
|Icom CM-60 schematic
|Icom CM-60 Schematic.pdf
The H12 may have completely different crystal frequencies than listed; these were often custom ordered for a given customer. If you're modding one make sure you check the actual crystals in your unit.
I suspect the Icom IC-M12 marine radio is basically the same rig with a different face plate.