Unless you change the rear, or install an overdrive, the engine speed will be the same. Its probably safer (for the motor) to run a 292 fast enough to run a 6000 series truck 60 mph than it is to do so with a splash oiler, but I'd start to worry about stopping it from that speed.
I've never heard of a ratio swap for a 2-ton. Someone here swapped early hubs onto a later axle to change the ratio while keeping the early wheels, but that looked like quite a project!
And when he was done he still had 50-year-old brakes...
There are some later 10 hole wheels that are supposed to fit these trucks. I've thought about finding a set of those wheels, and then swapping the rear that goes with them under my 6400.
But my 6400 was dented by a falling tree a week ago, and I'm now wondering if it survived.
