stay away from the ax-15s, a mild v6 could kill those. The NV3500s would be an ok choice behind a mild small block. Just something to keep in mind, is that the nv3500s use an integrated bellhousing. Anything over 300-325rwhp and the NV is on borrowed time unless you baby it. My s/c v8 dakota was dynoed at 355rwhp and was sometimes hard to go into gear under hard acceleration. Keep in mind also that the gear ratios flat out suck in a performance aspect. The NV4500 out of the rams are supposed to handle more torque, and have a removable bellhousing. But again the ratios aren't great