We've been in a 6-3 all season.  It's been very successful.  The #1 team tore us up with their jet sweep, off tackle action.  Looking at a 4-4 as a change-up defense that allows us to remain much the same.
This is an additional D, not a replacement.  We will still base out of 63.

We are small in our league, a couple great athletes, alot of good athletes.  We play with great attitude.  Lots of ball hawks, even if they don't have high ability.

In our 6-3.  Here are our position setups.

Mike - #2 D player.  Smartest, and great nose for the ball.  Good speed.  Not real Big.  Sure tackler.
W LB - #1 Athlete.  Athletic ball-hawk, plays slow if he needs to think.  (That's why he isn't the Mike)
S LB - Younger LB.  Good nose for the ball.  Solid tackler, decent speed.  Has "Want to"
W DE - Small kid.  Built like a CB, but super aggressive, so he is really good at attacking the edge.
S DE - Big Kid.  (My RG for UBSW) Does good at compressing sweep and blowing up lead blockers.
Note - As you can see, i balanced my D, by putting my best kid on the W OLB along with my smaller DE.  My best DE is matched with my smaller LB.
W DT - Oldest kid.  Big tall, aggressive.  Best with hand in dirt.
S DT - Similar to W DT, 1st year playing, he has progressed well and does a great job of attacking through the line.
DGs - I rotate here.  I have a couple younger kids that start here, that will be good DEs/DTs next season.  Rotate about 6 kids in here.
CBs - One CB is a long fast kid, decent tackler.  Natural Safety.  I have 2-3 more kids that are kinda all the same.  Not real fast, but good tacklers and can read and play the ball well.

My thoughts are basically, when i switch to the 4-4 stack.  The natural thing is to just move my DEs to OLB.  The biggest threat against us from the #1 team is sweep, off tackle, and counter out of their jet-sweep.  Essentially every formation consists of a play with a QB keeper option off of it.  Based on my kid descriptions above, see what you think about my position moves.

Looking to put my 2 best defenders at the OLB spots.  Then my S LB and my big S DE at Mike and Will.  DT's become the DEs, DGs, the DTs.  My Speed CB is moving to Safety.  The W DE will go back to CB.

So after that big diatribe.  My tendency is to put my top athlete at R (WOLB), my smaller younger LB at Will, my Big Smart Aggressive DE at Mike, and my 63 Mike at S (SOLB).

I appreciate your thoughts.