Al, I tried to run a 3.40 rear gear ratio in my '32 Ford roadster with an engine similar to yours, slighhtly taller tires and a 2004R trans. In overdrive at legal freeway speeds the engine was lugging way below its comfortable operating range. Changing to a 3.80 gear solved the problem and it pulls the OD gear easily on the freeway or open road.
For purposes of comparison my engine is a 350 SBC, Edelbrock 70cc heads yielding 9:1 compression, Performer manifold and optimized 600 CFM carb, Crane camshaft with duration at .050 of 218* and 230*, tires are 285/70-15 and a tight converter.
I hope this helps.
