One thing to keep in mind, and Don's idea works well for this, is to have a temporary base installed until you finish. I have a two foot long chunk of 3/4" plywood that I've used for years. It has a centerline drawn on it and as many pairs of holes down the middle as I've needed. It's also wide enough so that I can use it as a baseline to measure the height of stuff all around, like boot toppings. And of course it's covered in paint and glue drips, pieces of blue tape etc.
Thinking some more abt Don's trick, one of the challenges in the way I (and most people) set this up is that with two pedestals of fixed length, you need to find the right two spots on the hull. I suspect that model companies tend to default to a level keel more often than reality, but it needs to be studied before deciding on the spacing. The ability to adjust the level would be useful...