D Scott, is your recoil lug flat with nice edges or are the edges cupped? If it is cupped the rifle will shoot fine, but if you bed it, then it can be an issue going in and out of the stock. Normally Savage's recoil lugs are stamped and not machined. An after market lug is nice, Jim Briggs sells about the best finished one out there. I have a large shank model 12 repeater that came with a nice thick lug, but it's still a stamped one. I have a .223 1-8 twist on this action that is used for FTR mid-range, the lug does not hurt the accuracy of this rifle, if anything I do.
As far as mating chromoly to stainless, we all do it, all the time. Just make sure when you put it together you use some sort of anti- seize on the threads and put a little on the face of the action. This will prevent galling. When it comes to headspacing the barrel you can do it either way, brass or gauges, BUT YOU NEED TO DO IT RIGHT. Not to scare you but this is as important as building a round of ammo. If you've done one before then disregard that statement, If you haven't and know someone that has, ask them to give you a hand. If I'm using brass I like to have a piece that has been shot in a sammi spec chamber, then I full lenght size it with .002 shoulder setback for a go gauge, then I put a piece of scotch tape that is between .002-.003 on the casehead and use as a no-go.