I think Marshman is a fat guy who doesn't cut weight like a UFC fighter, meaning he diets down to 185 and doesn't put weight back on in time for re-entering the cage.
I read that Che walks around at 190 so probably will be the smaller man, but I expect he will be far more athletic and explosive than Marshman.
As for the fight, Marshman is not what I'd call a smart fighter, he's been KO'd twice (Pascu, Azaitar) by fighters who were technically well behind him but were able to land the right punch at the right moment. I'd also say neither have great
cardio or submission games (both won their last fight by sub however), it can of course go either way but I'm going for Mills by TKO, possibly knees from the clinch and then punches probably in the third round when they're both tired.