I inherited a 1957 Ranchero with a 312 Y-block. I'm having troubles getting it to run right. Put on a new distributor cap, cleaned the points and rotor, cleaned the plugs, new plug wires, set the dwell, and new fuel filter from the pump to the carburetor. The idle is good but it wants to slightly stall when I give it gas from a stop and then erratically cuts out. I tried to set the timing but the distributor is locked in. I have tried wd40 and PB blaster for a week. The only modification I can find is the original carburetor.
Tedward

Keep soaking the Distributor for a few more Days. Try moving it with the engine fully warmed up. Heat expansion should free it up. Not an unusual problem if the Distributor hasn't been moved in Years. Have you verified that the timing is advancing as the RPM increases? Use a timing Light and see if the Timing marks change. Maybe the Advance Mechanism is seized from lack of use.

  

sounds like your carb.

Suggestions are helpful.   I wouldn't mess with the timing anymore till you find out if the carb is plugged up.   Or if the accelerator pump has failed.   What carb is on it?

The carb s an Edelbrock 1406.,

I'm going to get a rebuild kit for the carburetor and not worry about the timing for now but, keep soaking it. The vacuum advance is working. And, thanks for the help.

TIP-IN HESITATION (Old Tech)

1) Accel Pump - Diaphragm and/or ADJ
2) Vacuum Advance - Operation -
          Vacuum Source - Canister Integrity - Breaker Plate Movement
3) Manifold Vacuum Leak

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My experience with a stuck distributor: I was working on a relative's car with a 302. The distributor timing needed adjusting but was stuck. I soaked and tapped and twisted for about 2 weeks while I was working on other things, with no help. I put a strap around it and lifted the car off the ground with a hoist, still stuck. Finally, I thought of my air chisel. The second burst it popped out of the engine. If all else fails, hit it with a blunt tool in an air chisel. I might ding up the base of the distributor, but it will loosen it. 

Sounds like this engine has been sitting for a long time.  If the distributor is that stuck in the block, I'll bet the vacuum advance is frozen as well. This could be easily verified with a timing light.  When you finally pull out the distributor, the oil pump rod will most likely be sticking out the bottom of it.  If this happens, the clip has fallen into the pan.  You will most likely need to pull the pan to clean it out.  The engine probably needs a value job too.  Is your intention to get the car running so you can sell it or do you want it to be reliable?   You may get it driveable without a lot of effort.  Making it reliable will require some effort and expense.  If your car is an original 312 Ranchero, it has some value. It also would have come with a Holley 4 barrel carb. The vin would have a "D" engine code.  Check the vin.

The vin# is G7RF204909. We want to keep it and use it as a back up car, it'll get driven once a month 10 mile round trip. It did sit for 11 years in a garage. I have the original carb.

I rebuilt the carburetor with a new kit and it still runs bad (a lot of cutting out, no back firing though).

Getting really frustrated.

Tedward