IMO, I would look at the different ARMS 40 series of BUIS. Thats just my opinion, in this forum, you will have many, many others who may suggest another one. I have 2 Bushmaster AR's. One is a carry handle ( A2 ), the other is a flat top. Both are the 16 in barrel M4 type. I also have EOTech's on both. On the carry handle one I have the model 551 on a Bennie Coolie mount that puts the 551 between the front post / sight and the carry handle. On my flat top I have the 552 w/ no riser, a ARMS 40 low profile stand alone rear back up / flip up sight. The only modification I did to this one was put a bigger front sight post ( .040 ) that Bushmaster suggests.
Obviously, I do not if it would work or not for you, but in theory it sounds like it might. What I think you might have a problem seeing, through all of your details, is the front sight post going to be able to use your rear sight. I guess there is one way to find out, get your project together and see if it will work.
Good luck with your build, and I hope to hear back from ya in regards to your project here.