Well this is new. I tried timing my engine and noticed the distributor would not budge an inch even with the retaining nut off. I decided to yank it all together and replace and the upper half sheared off! I tried PB blaster for a week and no dice the thing does not even rotate still. I am open to ideas the engine is a 400 in an 1977 F150, anybody seen this before?

 

If it was stuck in that bad, probably going to have to pull the front cover. Not a terrible job. Good time to do a timing set though

 

If you can get channel locks or a pipe wrench around what is left, try twisting with that while tapping with a small hammer. Or maybe use a crow bar and pry up on the broken part while tapping.

 

I've had it happen in 2 different vehicles. It took multiple of cycles of heating the engine around the stub with a torch, spraying penetrating oil on it, tapping it for a few minutes to help the oil work in then trying to work it back and forth with a pipe wrench until it loosened up. After the last one, I now do the heat/oil /tap thing any time one even hints at giving me trouble. And whenever I install a dizzy, it gets coated liberally with anti seize to prevent it from happening again.

Is that a chain to an engine hoist? Wrap it around the stub and get some pulling force with it then tap it with a hammer.

 

Oh man! Not a good day. You may need to clean up the nasty mess around the hole and try a little torch action. Heat the block around the distributor stem (but avoid the stem proper) and maybe it'll come loose with the thermal growth of the block. No guarantees.

 

Yes, unfortunately a very common story especially with the 351M/400 blocks. For years that was the only engine I ever heard of that had this happen, but in the last ten years or so I've seen it happen now with just about every engine family.
What the others said about heating and cooling and worrying it loose, and also cleaning it up before you proceed any further.

Keep at it and as far as I know they all eventually come out. Some break like yours, some get lucky (like I did) and it only took a month or two of fiddling with it to finally worry it loose.
Ditto on the anti-seize too. Better yet, paint the distributor body before you install the new one. Just to help stave off the inevitable in the future.

Guessing it's part lack of oil getting up into that bore, part galvanic reaction (or is it electrolysis?) between the dissimilar metals, but it's a bear when it happens.
That reminds me... I've had one sitting inactive for awhile. Guess I'd better go out and see if I can still move it. I'm guessing since it has not been used it's probably fine. But I'm not going to leave that to chance now that this discussion has served as a reminder.

Good luck!

Paul