What to do?

What is the compression, if its pushing 11 to 1, I be extra careful switch cams - get a custom grind cam to bleed off some of the compression to run on pump gas

Some would say the 3.91 should go, my take is depends, if MPG is important then yes, 3.23 or 2.94's but the 340 will run all day at 70 mph even with those 3.91 gears and the 340 loves gearing / high rpm's

You might well want to pull the heads and see if they are dome pistons, that motor sounds built . Aluminum heads would be OK with 11 to 1