Out of those choices, I would use the XE 256H
http://www.compcams.com/Company/CC/c...x?csid=20&sb=2
You live at 5,000' ASL or so. And your static compression ratio is only 9.1. If you use a cam that's too big, your intake valve closing point will be fairly late. That means your cylinder pressures will be low. Cylinder pressure is what makes power and efficiency.
The Edelbrock cam is is what used to be called a "RV" cam. It's designed for heavy vehicles to try and make low end grunt, but also have no top end. No reason to use that in a Cobra.
The 268H closes the intake valve at 60* ABDC. That will bleed off some pressure. And, it's a single pattern cam. SBF's generally do better with dual pattern.
The 256H closes the valve earlier at 56* ABDC. That will help build pressure. And it's a dual pattern cam. I would suggest using a 1.7 rocker for a little more valve lift; if your heads can handle it.