Comp Cams XR280r thoughts to given combo

At what rpm would peak horsepower and torque be?
With unported RPMs, the RPM intake and that cam my bet is 5600-5700ish neighborhood provided the springs are right. 1-3/4" headers will work for you but they're a little on the small side.

Would this be an easy cam on valve train?
Easy compared to what? It's a solid roller cam and from the 'Xtreme Energy' series at that......in other words probably not.
So shoot for an idle speed on the higher side and keep an eye on things.

Any input, thoughts, recommendations would be highly appreciated. Thanks
I'd just add, don't even think about running Cooper/BFG/street radials...get some M/T or Nitto drag radials at a minimum. Good tires made a big difference with my 505" B-body.
Being able to spin the tires at any speed sounds good on the internet, (and the kids love it:D) but it's pretty lame, getting beat off the stoplights by every other car on the road because of lack of traction...and sometimes just plain dangerous.

Now, despite my negative nancy attitude I think that will be a heckuva fun beast on the street in a Dart, with your gearing/tire combo... I like the cam choice for a nice street 451. That's gonna be a rocket!