71 c10 w/350 quit running on the freeway and won't start

Coil, coil wire, distributor rotor, electrical, broken timing chain are all possible causes. You need to determine if you have spark and if not, determine why.

I would think a broken timing chain would make some noise when it happened. Truck acted like I just shut it off. I had new plugs, points, condenser, rotor, distributor cap, plug wires, alternator, voltage regulator all done about 8 months ago. rebuilt carb 1 month ago. I'll check for spark as you recommended.

Not saying it was the timing chain, but listing the possibilities. If you find you have spark and fuel the next step is a compression test. You seem to have fuel as verified by seeing fuel squirting into the carburetor. Keep us posted as to what you find. Heck it could even be an issue with the ignition switch.

Yeah, actually on most older American made motors a broken timing chain can fail noiselessly. It all depends on valve clearance inside the cylinder. Most older American engines have enough valve clearance to miss hitting the piston at TDC. Even then you would have briefly heard at least one of the cylinders blowing it's compression back through the intake manifold with backfire. The only other sound you most likely would hear would be the chain clanging around inside the housing. But I agree with Bob on the rest of his list of possible causes. Since you were running and the engine just died (I'm assuming instantly - it didn't "sputter" to a stop) this is electrical. More specifically - from 12v to the coil to the spark at the plugs. There are a number of things in between that might have failed which include; the coil, the HEI module under the rotor (this rarely fails with a complete open circuit but it CAN), the contact on the rotor itself, the capacitor connected to the HEI module (more common than a failed module). If you have the original ignition; a broken points contactor (little brass nub falls out of it's mount(rare but possible)) Even the ignition switch mounted on the steering column can fail in an instant (can happen on an '82 C10 - I'm not sure how the ignition voltage is supplied to the coil on a '71) ... what ever it is, it HAS to be common to all cylinders. A marginal plastic connector at the distributor/coil that can vibrate loose has been known to cause this (in my experience), or a broken coil winding, even. If you don't have one , borrow or by a volt meter and start checking one item at a time until you find where you are loosing ignition voltage.