Surging can be too much timing at cruise speed. Can also be a lean condition at cruise.

Give us more info on the carb.
Main jets
Power valve setting (ie 5.5, 6.5,7.5 ect)
secondary plate size.

Do you know what the timing is doing?
@ 3500 rpm , no vac, what is it

Inliner Member 1716
65 Chevelle Wagon and 41 Hudson Pickup
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