Slant 6 engine ignition timing stays retarded.

Might also check that the distributor gear has been properly installed. When installing the gear, there is sometimes is a hole that is already in the gear the you do NOT use. Some people mistakenly used it to install a new gear. Been a while, but I believe that there are a shim washers and you use a feeler guage (.0100?) to set some clearance between the nylon gear and distribtor body. Also, I believe the tip of the rotor should be inline with the tip of a tooth on the gear.