For technicals I've used the various recce jeeps less some points, or the jeeps with recoilless rifles found in the various lists. They don't tend to last long or do much but they are mobile and kind of threatening!
Depending on how good you think the 1960's US Army is, I'd just keep the C&C elements (doctrine, CV's, special rules) and knock some stats for the units in the FWC calculator (I'd guess make them a bit worse than they are in CWC to show the power of Martian Tech off to the best!), and call them Primitive Tech and the Martians Advanced.
Should be fun
