Hey, forgot to mention (bit off topic actually), but I'll most likely be building a replica of sorts of a vietnam era M40 myself over the course of this year. It is the only one that I can put together cheap enough (minus optics). I plan on getting a new SPS Varmint (small varmint caliber as I alreay have done the .308 thing). I'll have to take 2" off of the barrel (yeah I won't even get close to owning a correctly serial numbered action). I'll then pillar and glass bed it in a correct looking stock (Numerich 553690), install the swivels, and I already have the sling. I do have an older Redfield, not an Accurange, but I can't afford one of those, and a Redfield base and rings.
I will not clip slot it as I have no use for that (and I'm not going to be building an exact clone either). I'm figuring about $450 for the rifle, $180 for the stock, $50 for the cut and re-crown, $50 for the rings and base, $30 for the pillars, and the rest of the stuff I already have, so about $760 total. Well, maybe more because my '06 will be without a scope.
It won't be super close, especially to a collector. But for something to have a close enough look and feel while I'm out plinking around it should make for a nice project. Good luck with yours!