Thanks for all the encouragement. I did not mean to be confusing...I had set the carb idle air/fuel ratio, but have not checked the cruise A/F ratio. The choke was open for sure, I cheated on the tire pressure with 46/42 psi front/rear. Tires had not been aligned yet, they were toed out a little, but another snow storm was coming and I wanted to get the run in before the roads turned icy. At 60 mph the engine was turning at 2780 rpm according to internet calculators (22 inch diam tire, 3.7 axle ratio, 5th gear ratio is 0.82).
I'm in Bozeman, drove over Bozeman Pass to Big Timber and back using the highway markers to verify distances.
Ignition timing set at 10 degrees advanced with factory electronic ignition advance curve.

I noticed the mpg carburetor has a smaller primary throttle bore than "normal" A14 carb. My other Datsun, a 1976 B210 Coupe with A12 engine and 3.89 axle gears has a little quicker acceleration and higher cruise speed (85 vs 75 mph)at maximum throttle opening on the primary bore only. The A12 has 10:1 compression also.
I was a factory trained Datsun mechanic back in the late 70's, its fun messing around with the Datsuns again..they are a great little car:)