Those 30 cals are NOT heavy recoiling calibers. Just get a fixed power scope of long eye relief (4"+) and mount it as far forward as you can, and still see the full field of view. The problem with variable-power scopes is that the eye relief decreases when you crank up the power.
I have a Leupold compact 4X on my Ruger No. 1 .45/70, and it has 58 foot-pounds of recoil. It has never cut my eyebrow.
Or, if you do get a variable power scope, get one that offers good eye relief over the entire magnification range, with a minimal shift in eye relief as the power level changes. Some cheaper scopes have very little eye relief and/or the eye relief changes a lot (shortens) when you crank the power up. Since you're investing in a custom gun, I'd assume that you have some money to spend on the optics that tops a fine custom rifle. I'd strongly suggest that you look at the scopes in the $350-500 range MINIMUM like the Nikon Monarchs (one of my favorite brands), Leupold VX-3 (which are known for generous eye relief, btw), Bushnell Elite 4200 (good glass for a reasonable price), or (my new all-time favorite) the Zeiss Conquest (the 3-9x40mm, which is an excellent scope, runs in the low $400's to mid $500's).
No sense building a very expensive rifle and putting mediocre glass on it. Good scopes cost money, but I'd rather have a good scope on a cheap rifle than the other way around.
Mike