I have a 551 F and a Larue mount (From C4i Grant ) on an A3 flat top . I am looking at the Larue BUIS. My question is..
If I am zeroed with my carry handle, and want to put the Eotech w/ mount and BUIS on, will I have to make elevation changes to my front sight post to retain zero w/ the BUIS/Eo setup? I am trying to figure out a way to change between the Eotech setup w/ BUIS, and carry handle without adjusting the front sight post.
I would go w/ the LMT BUIS, but I dont think it will co witness with the Eo/ Larue mount.

Why must you have a carry handle?  Why not just use the LaRue BUIS full time?  That is what I do.  And you are right the LMT takes up to much space on the rail to work with the EOthing mount.

Agreed.  lose the carry handle.  Just get a LaRue BUIS and use it full time, even if the EOTech is not mounted.  When I first got a flattop, I kept a carry handle around because I thought I would like to switch back from time to time.  I never used it as I never wanted to check zero/rezero after each time switching them out.  I eventually just got rid of the carry handle.  

Well, you MAY be able to do it if you don't have to lower the elevation on the carry handle too much (to the point it bottoms out before you reach zero).

-First thing, Zero the front post w/ the BUIS (since it's elevation is fixed).
-Then sight in the handle using only the rear elevation only. If it doesn't bottom out, you can zero it and then adjust the elevation index so the range markings are lined up. I suppose if it did bottom out, you could take a file to the bottom of the rear sight base and get it to work.

Honestly, I just ditched my carry handle for an EOTech w/ LaRue mount and LaRue BUIS, and could NOT be happier!  See ya later, Carry Handle! Now.... two more weeks and my 20" HBAR gets swapped for an M4 profile 16" and the A2 stock for tele-stock and hello 3-gun matches! :)

rvb