I have a Bushmaster heavy barrel carbine model number BCWA3F16 and an Aimpoint Comp M3. I would like to mount the Aimpoint on the upper receiver to absolute cowitness with the front sight post. I was considering using the A.R.M.S.® #22M68 Throw Lever Ring to mount the Aimpoint. But I believe a spacer is needed to raise the Aimpoint up to the front sight post and was looking at the A.R.M.S.® #38 STD SWAN® Sleeve which would raise the Aimpoint 1/2 inch. I'm particularly concerned with the height. Does anyone know if these ARMS products will go together to get me that absolute co-witness?