I did some quick calculating with you .82 od ratio and looks like 70 MPH is about 2200 rpm. Not bad.
Looking at my dyno charts on this page
https://www.12bolt.com/65279inline-cylinder-head-flow65279.htmlThe bolt in lump kit will give you a additional 10+ Ft Lbs TQ across the RPM range.
If using a mechanical fan, it can be changed out for a electric fan for greater efficiency of the engine.
Optimal timing can also help out.