Ooooo now this is my field! Yes Neca are officially 7 inch scale. But! The colonial marines are a tad on the smaller side as with all of the older Neca figures. The newer Neca figures (like from Back to the Future) are a bit larger. Scale creep, it's inevitable. McFarlane is also 7 inch. They're on the bigger side of the scale, similar to the newer Neca stuff. But they all still fit well with each other! The older and the newer Neca stuff plus the McFarlane figures. Also, Diamond Select has a lot of good stuff in scale with the figures. ZD toys Warmachine also works as a battle synth. A bit on the smaller side of 7 inch scale. The latest movie Warmonger (Ironman) from Marvel Legends also is a good base for the Berserker suit. Some of the largest and bulkiest G. I. Joe figures can work as well, like Gung Ho and Roadblock, they can pass for shorter muscular dudes with the marines.
Wrestling figures! Their heads are good for new the new faces your marines will be carrying. There are two main lines (2 different companies) that make them, but their scaling is all over the place. The best you can do is buy a bunch of them in a bundle and more than half will be the right scale. The bigger ones I use on Michael Myres and Jason Voorhees bodies as the marine maintenance engineers.
Bad news though, not all of the heads in the Neca line itself use the same peg... You're gonna have to drill to get these heads on the same peg.
