Rob Ryan didn't install the 3-4 in Dallas. It had been in place long before he got there via Wade Phillips. The reason Ryans defense regressed against the run can be attributed to losing Sean Lee, Bruce Carter and Jay Ratliff for most of 2012. The improvement in the secondary and passing defense came via adding Brandon Carr and Morris Claiborne.

Take any defense and remove the top 3 players versus the rush and add two top tier secondary players and you will see the same result. This is absolutely nothing to do with Rob Ryan.

I have no issue with Grantham as a candidate although his defense also regressed much the way Ryan's did in Oakland. I think he would require surrounding himself with positional coaches with more NFL experience to avoid tripfalls, but I don't see the relevance of the 3-4 installation arguement. If that is the case, Crennell is the clear cut best candidate.

He installed his own "version".... Did not continue with Wade Phillips 3-4...

So yes, he installed a 3-4.

One of the pleasures of Cowboys camp is watching Rob Ryan install his version of the 3-4. It's a far more motion-based version, compared to Wade Phillips'. Thus far, Ryan has stuck to the templates he established in Cleveland. Look for base 3-4s on early downs. When Ryan gets an offense into passing situations, or when he's facing a spread offense that used three or more receivers as a base, look for Ryan to go ''psycho.''
Dallas Cowboys News & Analysis | Cowboys Nation: Rob Ryan -- Psycho Like a Fox?

The Nose
“The nose is obviously a run player, gives you some stops inside. You like to have a guy who can move a little bit because you’re going to move him around.”


Defensive Ends
“Ends are your guys who are going to anchor the C gap or the B gap based on the formation. C gap is outside the tackle or outside the guard. They’re gonna anchor those and they’re going to generate your inside pass rush.”


Outside Linebackers
“Your Sam and Will are the outside guys. They’re gonna be the guys who should be your most productive guys because you’re trying to get those guys on backs and generally they’re pretty athletic. They are also going to have some coverage responsibility but pass rush is real premium with those guys.”


Inside Linebackers
“Inside backers, Mike and Moe, are pretty much the glue as far as making the calls, getting guys lined up. You need a guy in there who’s a thumper, who can be real physical. You also need a guy who can cover a little bit and scrape inside out on the ball. That’s pretty much your inside guys.”


Cornerbacks
“You like to have guys who can play man coverage. You like to have guys that have some awareness to take away the proper leverages and be able to reroute guys and as a general rule, I think it’s real important that all guys in coverage are rerouting guys from disrupting. Don’t let guys have what I call free access into the defense which means don’t let guys run free — you got to reroute guys”


Safeties
“Your safeties (free and strong) are guys that gotta be able to come down and play the run when you play an eight-man front, they’ve got to be able to come down and cover guys, and then they’ve got to be able to give you a little pressure when you call their name. So we put a lot of things on those guys.”

In my opinion the talent on hand fits this scheme much better than a 4-3.

neither is great at coverage but can probably cover "a little bit."

Yeah, especially the quote about the ILBs - both Lofton and Hawthorne are thumpers who have led the league in tackles over the past couple of seasons, neither is great at coverage but can probably cover "a little bit."

I hope Hawthorne can make the coverage calls because Lofton doesn't do it.