Unless I am mistaken, there were no egr systems back then. I thought the first egr systems came about in the early 1970's.
Of course, I have been known to be wrong sometimes.

 

I had very similar symptoms in a car once, turned out to be a blocked up muffler.

 

These trucks definitely never had an EGR system originally. If the engine was replaced with a more modern powerplant then perhaps it could have an EGR system.

 

I also vote for a plugged muffler or a collapsed pipe
slowing or stopping the exhaust to properly exit the engine.

 

hey all, maybe not technically an EGR, but don't they have a heated port under the carb fed with heat from the exhaust?

 

Yes there is a manifold heating port.

No, no egr, other than what leaks out of that exhaust crossover pipe in front of the motor which in turn gets sucked into the air cleaner....

I vote for clogged exhaust, with the possibility of a stuck valve or two thrown in.

 

Ditto on that!

 

Maybe some squirrels or chippies packed your pipe and it's not breathing too well. I think Pinecone ford had some issues like that. My father in law had a 2N and they filled the exhaust all the way to the manifold.

 

I had a problem once, not with smoke but I couldn't figure why my motor always ran rough at low RPMs I did not realize the distributer on a Ford turns counter clockwise. So even though I had everything right in my mind it wasn't. From what I've been reading on this thread there are mostly two schools of thought , electrical (timing, plug wires etc.), or critter nest ( plus a thought of stuck valve). If you already know the distributor turns counter clockwise and that is all good, can you loosen the tailpipe at the header, it would at least eliminate any chance of a clog from the header back, or maybe pull the plugs for a peak and a compression test. Im sure not the sharpest pencil in the box, but I just thought Id throw in my 2 cents. I have read mice getting all the way past the valves into a cylinder. Best of luck with this, im interested to see what it ends up being.

 

What Jim said.

 

^ x2

Check the compression. Im betting there is an Intake Valve that is stickiny and causing some blow-back thru the intake. Also, check what everyone else recommended, plugs,timing,muffler etc