I would do as subgauge recomended. Build the stock up to where it needs to be with bondo. Duplicators do not get them exact either and some material will still need to be removed. If the guy is good with it he should be able to as much material behind as you request. So where the side plates are have him leave a little bit more than what is missing. I would recommend making a smoke pot to blacken your parts to show what needs to be inleted. Also get a couple of inletting scrapers like those sold by Brownells or Midway. Jerry Fisher and Royal Arms are the brands. I like the Jerry Fisher ones best.
For your first stock I would highly recommend trying to get a duplicated one to inlet. There is a lot to keep in mind while turning a block of wood into a stock. You have a very nice piece of wood and I am sure you do not want to screw it up.
