By meaning across, you mean directly above it I'm assuming. I wasn't thinking about 2"(1.5" for my 2G) yet. I was going to leave the original jets in there and just shim it with 2 shims and adjust the mixture screws for my Muzzy slip on before I decide which jet kit to go with. This way it should tide me over for a few months while I decide.
The reason for me drilling say a couple of 1/4" holes is to try and experiment with say 3 or 4 shims and a couple of holes for an extra bit of horsepower. And you're completly right if it doesn't work out duct taping over a couple of 1/4 " holes should be no problem. When I pick which kit I want I'll make sure to drill the 1.5" hole or Ivan's many Holes where the "tester" holes I made are so it's nice and clean.
Remember, everyone repeat after me.....duct tape is my friend....duct tape is my friend!!