50/50 regular old green stuff. Don't use the pink/orange or the gold, those are for late models and can damage the pump. The "mix with anything" will be fine, too. If you can find it, get the full strength stuff and cut it yourself. I find that the "pre-mix" is a little weak for my tastes.
Side note, I didn't drill a releif hole in my theremostat, and have had no issues with air in the block/head, however, it won't hurt anything to do so. There are even thermostats on the market that have a hole already in them.
one more thing-pour it slow. Don't rush it, just go nuce and easy. That will help allow the air to purge out. If you listen to it, you should be able to hear the air comming out at the filler neck.
