the 107 number on your cam..
go to 106 for a more radical sound
110 112 for a smoother idle...
just for reference. as you look at cams..
we are not talking/adressing performance in this answer...only idle quality..

Imho if its a street car..look for lower mid range power/increases and anything that increases cyl pressure on those dished low compression pistons that 400 comes with..
(in your scenario) increasing head flow at this point isnt going to give you a gain in low rpm performance. vrs money spent.
but the right cam and intake sure will....

unless your 48k converter and 4.56 and planning on revving it all the time to find power.

fwiw