That transmission is more commonly referred to as a SM465. As far as removing the PTO your dead on, just unbolt it and slap a cover plate over the hole. You should be able to get a PTo cover plate at any junkyard. The ones off of chevy transfer cases should work as well, if you have trouble getting one off of a tranny.
1973 K20 - 350/465(as of 10-04-03)/205