The big Maico engine eventually got water cooling and was produced by various people under M-Star, Maico, ATK. Highland even slapped their logo on a couple, during that weird ATK/HIghland deal. There's probably more of them around than we realize, some Dutch sidecar racing company bought up all the equipment/IP when Maico went under and kept on making things. I've sat on one of the ATK/Highland 700s, but they didn't have it running that day as they were more focused on demo'ing their new 4 stroke bikes and quad.
CC's ranging from 500-620-700+ all based off the same basic bottom end.