This is on a 86 E150 6cyl 300 carb'd 4spd manual van...

After changing the cap, rotor, pickup, and plugs and wires, and putting the distributer back in the motor (it had to be removed to change the pickup) the motor would not run.... but it would run if the distributer was turned almost 1/3 a turn from where it was originally.

Since nothing at all was changed (only replaced with exact replacements, and the distributer position was marked when removing) could something be reassembled incorrectly? Is there a simple explanation for this, or is it obvious to someone else what was done wrong?

Any thoughts...?

 

Sounds a little like the distributor is a tooth off. The helical distributor gear needs some lead when dropping back in to get everything lined up.

 

You probably were off a little when you reinstalled the distributor. If you can get it running, put a vacuum gauge on direct manifold vacuum.
While it's running, disconnect the computer controlled advance (I believe that's the plug on the side of the distributor, someone may correct me), rotate the distributor to advance the timing until you get the maximum vacuum reading possible. Then, retard the timing until the vacuum drops down to around 1 to 1 1/2 hg less than the peak reading you got.

Hook up your advance again, and leave it.

 

If it's possible to advance the timing into spec it could be left alone. Depending on the engine though, the distributor body will hit something before it can be turned far enough.