I think the 380c version of that motor will not need an adapter plate. Even if you decide not to get the 380 6s, the lehner 5300 is the next best motor for your app. Whatever you do, do not get the 540 6s. I have both the ss5800 and the 540 6s so I know. The 540s is noticeably faster, but acceleration is about the same if not worse than the novak.
Check out my custom converted 8ight:
Sub 7lb, lowest CG of any 1/8 buggy