Well, the 70-grainers ought to shoot with that twist at least.
First thing to do is to check and make sure all the scope mounting screws are tight. That includes the ring screws, the dovetail clamp screws and the base screws. Sounds like you already did that. Barrel screwed into receiver tight? Holes in target are round? Crown on muzzle has no dings? Ammuntion has decent runout out of dies? Ammunition still has decent runout (use dummy round!) after trip in and out of chamber?
The thing that gets people with custom stocks is variations in the thickness of the stock and screw specifications.
If the stock is vertically shorter than the factory stock, when you tighten the screws, it might be that all you are doing is clamping the magazine between the triggerguard and the receiver without ever grabbing the stock. So the action rattles around and you get oversize groups. Even if you bed it, it probably won't be tight enough. The solution is to take some height off the magazine, which should be a free-floater between the triggerguard and the receiver. If the magazine is integral with the triggerguard, there should be clearance between it and where it contacts the receiver. If you can remove the magazine and test fire it as a single shot with the screws reasonably tight between the triggerguard and the receiver, you can check to see if that is the problem.
If the screws are too long for the new custom vertically shorter stock, they may bottom in the holes (depends on receiver design) before they clamp the triggerguard and the receiver in the stock. To fix this you take some length off the bottom of the screws as needed. I try to be 1/4 to 1/2 turn short of the bottom of the hole when tight. Make sure the bottom of the hole is not filled with junk left over from inletting or bedding.
If the screws have some shank above the threads that is of a greater diameter than the threads, the shank won't enter the hole in the receiver, and maybe the receiver and triggerguard won't clamp the stock between them. For this problem you can switch to screws with less shank and more thread, or (sigh) get the die and the die stock out and cut threads on the shank.
3-4" groups sound like something is loose somewhere, especially after you have switched scopes to one you know is reliable. Let us know what you found when you get it to shoot.
Saving money on haircuts means you can afford more gun stuff. Keep pulling....