Heater core

Hi!

I'm planning to replace the heater core on my 67 dodge dart GT next weekend, and have a few questions.

Do I have to bleed the system aften replacing it? If so, what is the proper way to do this? I have a non-factory radiator, and I think theres no bleeding skrew. Can i just leave the top cap open for a little while?

EDIT: I have a Champion radiator.