Jeff,
My truck's drivetrain is original EVERYTHING (engine, trans, rear end, brakes) and I've been on the interstate at 65 mph for over 100 miles. I've done several 50+ mile each way trips on the interstate at 65. No problems whatsoever.
The truck is a 1966 1/2 ton stepside. Original 230, 3 speed column, 3.73 rear end. The 230 has a short stroke and 7 main bearings so turning 3k continuously is no big deal.
Since my truck's a 1966, with a later drivetrain it's not exactly a "stovebolt". So my experience may be meaningless to you.
-ftyler
