I use thin wall brass tubing I buy at the hobby store by K&S Brass company. I forgot what size it is?? I just used my calipers to measure the hole dia and then went down and bought the closet size. I usually tap it into place and then grind it flush with the head on the ends of the holes and your done. I use epoxy glue also when inserting the tube just to help any intake leaks that might appear. The fit is so tight i do not think you would ever have one but you never know? I always put these in before i port the intake runner and then rough port the runner just till i can barely see the brass below the port wall and then polish it out with whatever grit I am using for that motor. I do not see why you can't install it now and maybe use some good A&B epoxy from a head porter or a head repair shop to build up the area you cut to low and blend it all back into shape after installing the tubes. The tubes really give you a great guide to max the port volume if that is what you are going after? My own ported heads flow pretty dam good i have to say using this trick. Hope this helps!
Jerry
