I have driven it around town and it's fine and have hit 40mph with the old engine. I now have a beefed up 235 with a 4 speed manual transmission so we are considering the suspension upgrade.
I wouldn't consider changing from lever action shocks to be an upgrade. The truck was designed to drive at about 60 mph. Nothing you do to it will make it handle like a modern car at 70 or 80mph.
Be content with 75 year old technology and drive within its limits. In my opinion, 60-65 mph is fast enough to drive on the freeway in a vehicle that's three quarters of a century old.
Do you still have the stock sized rims and tires? Larger diameter tires make high speed driving easier on the engine.
