couldn't you just test fit the grab irons int eh oles and see if they go in? if they give you trouble then you can take a pinvise and make the holes bigger. i'd use any model glue or cement, but you have to stick the grabiron in first, then glue it in from inside the shell. i learned this from expierence, cause i used to glue the grab iron first and try to slide it in, only to get glue smeared off the part and on to the shell. if the hole doesn't already go all the way in through the shell, then drill it in.
