just pulled 305 and put in a 350 the starter wants to continue to turn over even after the key has been pulled out only way to stop it is to pull off the battery cable it has done this with 3 different starters and 2 different ignition switches also used to do it intermittently with the 305 any help or ideas would be greatly appreciated

 

Possibly a short to positive on the solonoid lead. Also when you say you have changed the ignition switch do you mean the electrical switch under the dash or the key switch. Maybe there is a problem with the rod that connects the key switch to the electrical switch.

 

Yep, that was going to be my suggestion as well. Sounds like something is not hooked up properly to the starter.