Streetable on a 3.7? I could go look at the current dyno graphs and visualize some typical graphs from v8's. Look at the gain's per 100rpm increment on an engine with good flowing heads for it's displacement, devide by 8 and multiply by 6....and STILL end up guessing.
My wild stab at it for a 3.7. 20rwhp with no porting to the heads. That will set what rpm the peak hp will be and from there you can make more on either side of peak with port work.