Can someone guide me for a proper cam?

[Myasylum]

With the RPM heads, can I use the stock rockers and push rods? I may hold off on the cam for now.

 

[Curiousyellow71]

Well.....
They are suppose to.

As I see it... No harm in trying them. If you don't like something about the fit...buy rollers rockers and new pushrods.
Watch your pushrod length as it affects the lifter preload.

 

[70bigblockdodge]

With the piston down as far as it is in a 400 I would advance the cam at least 4° with a cheap +4, 0, -4 timing set. If you add almost any duration to a stock 400 cylinder pressure will fall lower than stock. A good intake and exhaust will wake it up. Very easy to over cam a 7.5:1 engine, tread lightly.
I currently own one that is overcammed with a 284/.484 Mopar performance cam, it is not a good driver, but runs great above 4000 rpm and the parts were free.