[Dave in MN]

John,
The lean condition happens at two throttle positions at speed in the higher gears (4th and overdrive) under mild load at the same engine rpm. It happens with the progressive linkage or the 1:1 non-progressive linkage. I have tried everything I have thought of to remedy the issue, but it sneaks back. A quick change of the throttle and it vanishes. I have been, and could live with it.

Thanks for the comment on the vent. I realized that need and will run the vent as high as I can get it under the hood hinge next to the tank. Eyeballing from the top of the proposed vent to the gas cap, I think I will lose about 1 gallon of capacity in the original tank because I will need to keep the level in the tank below the top of the vent, plus a margin for "slosh". I am toying with the idea of a vent with a float activated stop/vent plug. In the end, I think I will increase my capacity by 3.5 to 4 gallons of fuel without the vent stop and to a total of 16 gallons if the vent stop idea works out.
Thanks for your comments.

I'll keep my progress posted to this thread over the next two months as the parts arrive and are installed. I will post some photos of the equipment/installation.
Good Day!