Sounds like a good idea if you have the funds. In theory, the 38-55 or 375 should be an ideal cast bullet hunting cartridge -- if only we didn't have to struggle with the goofy dimensions.
Dave Manson does good work. I've also been pleased with http://www.pacifictoolandgauge.com
My only suggestion for the reamer design is to make sure you design it yourself. Don't leave it up to someone else assuming that they understand cast bullets, because usually they don't understand cast bullets.