I have a 63 dart (225) so what are the tricks to replacing the gasket. Any suggestions welcomed.

at least a few days in advance start soaking down all the mounting nuts / bolts with your favorite rust buster. Get the grime and goop out of the way so the spray has a chance to seep in, If driving the car during this time wait till the exhaust manifold fully cools before spraying, they crack real easy..
and
have a plan to replace the end splt castle nuts, they will certainly be froze to the studs,, and don't be surprised if a stud snaps,, have a plan there too.

Some of the studs go into the water jacket, I replaced one resulted in coolant everywhere. So don't be shocked if this happens.

This article provides some good info:
DD
http://www.slantsix.org/articles/Slant_ ... lation.htm