Being that the partial choke does not improve the condition, I am inclined to think it's an ignition problem.
Some things to check:
Worn distributor bushing causing the points to not remain set correctly. They can do some strange things, vary with RPM, temperature, etc.
Distributor cap and rotor. Have you checked the spark at the plugs? Could be loss through bad wires, rotor/cap connection, rotor or cap carbon tracked or rotor burned through.
Bad ignition switch or loose/corroded/mouse chewed/pinched/burned wire causing loss of power to the coil. Try temporarily connecting a volt meter from the + terminal on the coil to ground. Run it until the problem occurs and see if there is a voltage drop.
The quality of today's points and condensers is sometimes questionable. If there is some distributor shaft wear, or you suspect there may be a problem with the points, an electronic conversion can solve a lot of problems.
Other things to check not related to ignition problems:
Take a look at the valve train. Check the valve lash, look for a broken valve spring, sticking valve, dropped seat, bent push rod.
Is there any smoke when it misfires? Black smoke would indicate flooding carb, restricted air. White smoke, raw gas, eye burning smoke would indicate unburned fuel from lack of spark or loss of compression.
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Today's Featured Article - The 8N and the Fox - by Zane Sherman. Dec. 13 1998, Renfroe, Alabama. Last niht I dreamed about the day that I plowed the field of about 10 acres over on what Jimmy and Dandy called the Ledbetter field. I was driving the 1948 8N Ford tractor that Jimmy bought in 48 new This was prebably in about 1951 and maybe even befor the house was built. This would have made me to be about16 years old and I drove the tractor for nothing and would have paid to drive it if I had had any money which I didn't, but neit
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