I think you'd probably want one of the older versions of the aftermath. Before they used to be like 90% TM compatible but now people are saying 75-80% TM compatible.
Also you'd potentially be getting more reliability assuming it's a weaker spring. 370 is with .12's most likely but I wouldn't doubt if they used .20's and tossed in a stiffer spring. 300 is way too low though, you should be getting something in the 310-330 range (assuming .20's).
Best thing to do is not worry about it and chrono it yourself when you get it.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE