The normal 3 LB’s will likely be: Parsons, LVE, and Jaylon.
Let’s say this is how those 3 will be lining up (we really don’t know yet):
SAM - Micah Parsons
MIKE - LVE
WILL - Jaylon Smith
(Neal and Cox might be the two LB’s in the nickel package with only one of those two playing as the Dime LB).
When Quinn goes to the front that has the 34 “look”, they won’t bring in an additional LB because the fourth LB standing up on the end of the line will usually be Gregory. In those instances, you will usually have the SAM ‘backer and the LEO standing on the edge like 2 OLB’s. Those two would essentially become on ball LBs)
Like in this picture of the Seattle defense running the “34 look” defense:
In this example, the SAM (pink SLB in the pic) would be Parsons standing on the left side in a two point stance where he can rush or drop depending on what the coaches want.
The other guy on the edge would be the LEO (in red) which will almost certainly be Randy Gregory.
Those two would be on the ball, and of course the other two (MIKE and WILL) would be standing between them, playing off the ball. In the picture, Mike is positioned right behind the NT while the Will is lined up roughly on the 5 (outside shoulder of the OT).
So, my point is, even when the defense actually
is in that 34 look… they’re still going to have the same LB personnel in the game as they would with a 4 man line. Really, the only difference in the 34 and 43 in this instance would be that Gregory is standing up instead of being in a 3 point stance like he does for the 4 man line.