If you use the 3% nickel, it will stand out ugly and proud no matter if you blue or case color the action.  I use tie wire that I degrease with acetone and clean of oxidation using maroon scotchbrite before use.  Peter Nagel once told me that he uses wrought iron rod, but he has a limited stashed supply and can't get more.  As I recall that conversation, he said that tie wire was a bit better than coat hanger, and about as good as anything else you can get.  Not sure how much of that was humor, and how much was advice.  He also said that a good long annealing with the action shielded from oxygen using stainless steel wrap or carbon immersion was helpful to equalize the steels a bit, and keep the weld from showing in the finishing.

You'll want to set up some baffles on the underside and sides of the joint, and use an auxiliary feed of shielding gas underneath the weld, to keep oxygen out.  This old semi-steel/wrought iron in Remington's actions has an awful way of bubbling out carbon and crud just when you think you have it right, and the shielding gas around the weld area in addition to that on the tig torch helps minimize that, but you'll still get it.  

What I really should have said instead of the long winded stuff above, is just send it to Peter Nagel, and he'll do it right.   

On the other hand, if anybody under the age of about 60 wants to learn how to do this, and offer it as a service for the next 20 years, I'd heavily encourage them to learn it and do it; we need skilled trades to work on our guns, and we're all getting older and many of us checking out at an alarming rate.

You can't go wrong working with Pete!

have been tig welding for 25yrs steel alum ss magnesium sometimes as thin as .020  dont know everything didnt go to college so doing it is how i learn o and out of the 7 local welders probably the only one with 7 different tungstens in assorted sizes

I have an old hepburn action that had both tangs broken off when i got it, I forged new tangs from what I believe is electrolytic Iron that I got from and old mine. tig welded the tangs on using tie wire. I havenot colored the receiver yet but you cannot see the filler rod tangs in the bare action. 

     On another rescue hepburn I welded up the goobered up screw holes where someone had tried to drill out screws with maybe a hand drill and slipped off the screw and into the receiver and went about 1/16 inch in. for this i just ran som .030 mig wire out of the gun and used it for filler rod. again it cant be seen on the action in the white.