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.html
The 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.

Inliner Member 1716
65 Chevelle Wagon and 41 Hudson Pickup
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