As I can't find the Savage I want (Model 116 Bear Hunter in 300WM), due to it being a "build to order", it has been recommended that I build my own. Was told to start with a used 110/111 series receiver and go from there. So, as Savage rifles are totally new to me, I have a few questions:

By the Savage catalog, I know I need a long action receiver for 300WM.
Do I just go by the action screw dimensions of 5.062, common to all Savage long actions?

Looking at the FAQ section of the forum, there seem to have been receiver design changes over the years. Apparently some long actions had magazine openings only long enough for short action cartridges.
Should I stick with a particular range of calibers from the donor rifle?

I'll be prowling pawn shops and guns stores looking for a donor rifle.
Anything in particular to look for in the way of common problems with long action receivers?

This will be me started on my search. I can worry about bolt head configuration later.
Lastly, ANY advice appreciated.