But it's amusing-- Andy Reid's penchant for drafting undersized DTs who look like 3-4 DEs and undersized DEs who look like 3-4 OLBs actually puts them in a decent position to transition. I will say the fact that the Ravens and Pats recently switched to 4-3 centric alignments doesn't exactly make switching to a 3-4 "ahead of the curve"... but the two best defenses in the league (Texans and 49ers) still play the 3-4 and they play it well.
The one big piece they're missing of course is a true nosetackle--which is arguably the most important piece of this defense. Mike Patterson, the lone DT holdover from JJ's gap-control scheme, is probably the widest body they have and maybe he could add some weight and be a NT... but assuming they could address the NT via draft or free-agency, look at the other positions that are already in place:
DE: Fletcher Cox, Cedric Thornton, and Cullen Jenkins are all listed around 6'4" 300lbs... all of them are "lean" for that weight; Cox was projected by many draft gurus to be a 3-4 DE and Thornton has the same body type and skill set. Jenkins of course played 3-4 DE in Green Bay and was very effective-- the Packers are still missing his pass rush and it shows every time Matthews is injured. Jenkins has been less productive playing inside in Philadelphia.
OLB- Trent Cole can maybe lose 5-10lbs and function as the heavy "rush" LB, they can use him like the Ravens use Suggs, occasionally putting him in a 3-point stance as a true 4-3 DE. Most importantly, Brandon Graham IMO would be much better rushing upright from the outside position. At 6'0 260lbs, (same size as James Harrison) he'd be more effective given a running start to exploit his quickness and explosiveness. The faster a smaller man can move, the more force he can generate (momentum = mass x velocity). OTOH, Graham would be less of a liability in the running game if he could see the play develop off of the line before getting swallowed up by the OT. When tackles get their hands on him right away, lacks the reach to create separation, he has trouble holding the LOS and seeing into the backfield; he tends to get "swallowed up" and loses the edge. Now 3-4 OLBs usually only need limited coverage skills and really only play the hook or the flats, and I think Cole and Graham would be athletic enough to cover those areas when needed.
ILBs- We can get another year out of Ryans, I know he left Houston when they went 3-4 b/c Cushing was better, but his diminished quickness will be less of a factor in a 3-4 as he'll have less ground to cover in coverage. Kendricks could play the other ILB and take TEs in coverage in man-to-man situations. I know Kendricks isn't huge, but he's roughly the same size as Navorro Bowman, and Bowman looks good at ILB even after playing 4-3 OLB at Penn State.Obviously if they go in this direction, they'd want to draft another OLB like Jarvis Jones that's a pass-rush specialist, as well as a NT. If they stick with the 4-3, I think they should move Kendricks to WILL and get a taller SAM to cover tight ends. Either way, they need to get rid of "The Invisible Man" AKA Akeem Jordan. This guy has an incredible knack for NOT being around the football. Obviously, the secondary is a complete trainwreck-- soft guys who don't want to hit anyone-- and needs to be overhauled. But, how does everyone feel about the prospects of switching the front 7 to a 3-4 alignment?