If you already have a #1 you want to conversion is pretty easiy and straight forward.
Have Douglas or any other maker chamber the barrel, Douglas and Shilen can also supply a factory profiled barrel and cut the threads and extractor cut. Think it'll probably run you about $500+ by the time you get done and have the barrel fitted to the rifle by your smith. You might have to change the extractor based on what it started out as.
If you are thinking of getting a #1 and then doing the work it's a little different. If that were the case I would simply look for and pay the price for a factory rifle. #1s were chambered in 7.62x39 in a non catalog run of 500 rifles. These are "A"s Light Sporters with 22" light contour barrels, sights and the Alex Henry forearm. THey are stainless with walnut stocks.
The advantage is it would cost you roughly the same and NOT be a custom rifle. It would hold value and collectability, even if shot.
Right after you get done with the custom, it'll be a $500 used #1.
I don't think there is any need to send cases to Clymer. Surely they have and make SAAMI spec reamers. Do you really want a non SAAMI chamber??
Were you thinking of sending 3 fired cases to Redding or RCBS and having a custom reloading die made, rather than a chamber reamer??
Yes it would work just fine. That being said the factory rifles were very very slow sellers and many still show up NIB for sale and sadly seldom bring what the owners think they are worth.
Your quest sort of reminds me of the 17 Remington #1 I built. I started with a new factory 223 so the extractor wouldn't need to be changed. I had a Shilen Match grade barrel installed along with a Canjar trigger. I then installed a high power Leupold scope. One day my cousin , he built one too, and I were in a gun store discussing the 17 Remington with a guy that owned a Remington 700 in 17 Remington. We were complaining that we could no longer buy bulk Remington .17 caliber bullets from Midway and had to spend 3 cents more, per bullets for Hornadys. The guy got this quizical look on his face and then asked "Now lert me get this straight, you spent all that time and money to build a $2000+ rifle and you're bitching about 3
cents extra per bullet"? Yep, you have to control prices when you can.
While owning a 7.62x39 so you can shoot cheap factory ammo isn't a bad idea. Build a high dollar rifle to shoot cheap ammo, might not be the wisest decision you ever make. Then on the other hand if it's something you want and can rationalize, go for it.
As a personal observation I simply have no interest in a pointy 330--30 in a #1. But that's ME. ;-)