Compass Lake Engineering can turn your A2 upper into a flat top, with a permanently attached extended scope/target iron sight base that places the scope at the right height and gives plenty of adjustment for eye relief. HOWEVER, the A2 upper receiver converted this way will have a large round hole at the top rear behind the scope base which is left over from the A2 sights. The cost to do this was about $165, last I heard, and while this is the deluxe approach, either using an A1 upper (to avoid the hole) or just getting a flat top upper and adding a bolt-on scope base would be more practical. CLE makes a bolt-on scope base for flat tops that duplicates their permanently attached setup but does not have provisions for mounting target sights. (NRA Highpower Match Rifle aperture type.) This is of top quality and sells for $90 if memory serves. You would probably come out ahead to sell your A2 upper and buy a flat top and a GOOD quality scope base. One advantage of using a good bolt-on scope base is that you can very quickly change scopes from one flat top upper to another. Just undo 2 screws, re-zero the scope after installing on the new upper, and you're in business. Compass Lake Engineering can be reached at (850) 579-1208. The proprietors (Frank and Theresa White) have a great reputation for quality and value, are very helpful, and should be able to assist you with any AR15 related project. Their specialty is highly-accurate AR15's for Highpower competition and varminting. Hope helpful,
John