the one i got with my upper someone cut the top off to work with a scope(flat top upper)... i needed the full sight.. so i got a new taper pin base.. i drilled the base tapped it for set screws.. everything is great.. except... how to i line the new base straight up? what i want to do is set it up right then drill the barrel just a smidge so the set screw have a pocket to sit in... but i dont wanna drill it till its lined up...

help