Couple 440 Motorhome and 318 questions

I recently have had the opportunity to purchase one of my dream cars a Dodge Coronet 440. It currently has a 318 in it. Quite some time ago I purchased a 440 out of a motorhome to go into a 64 valiant. My question is really 2 fold.

First on the 440 is a "brake" on the tailshaft of the 904 transmission. What I would like to know is how do I deal with it? Does it need to be replaced? What needs to happen for it to be replaced?

Second I am now rethinking where the 440 will go so I am wanting to drop the 440 into the Coronet. Will the 440 bolt to the 318's transmission or should I just completely transplant the 318 and trans into the valiant and deal with the 440 trans? Any other gotchas with the 440 I should know about? I am hoping to hop the 440 up as money becomes available.