A stock 390 4V intake vs a preformer = Preformer wins. Flows better than stock, more responsive on takeoff. It would work well on street with stock 390. Change the heads, change the cam, change the carb and Preformer RPM will work better.

All depends what you use the 390 for. I had a screamer Merc Cyclone 390. When crossing a intersection long ago, a truck running a red light came at me broad side, I caught it out of the corner of my eye and tromped the little Merc. Today I have two fine daughters that could have died but did not all because that car would pull right off the bottom.