RE: Cox .074
No one that I know of has done the AME hop up mods to one of these. The standard is 17,000 with a 7x3 prop. APC has a good selection of props in the 6x4 size range if you are looking for more speed. These engines are so bulky that setting one up for a serious speed project does not make sense.
I think the main reason why there isn't much message traffic about hopped up .074s is because they run so well as is. Norvel never bothered to come out with an AME version of it.