Your right about pre and post heating the chrome moly. You must be a tig welder. Like you I have seen a lot of frames at the strip that were tig welder and run with out stress relief and no problems encountered.
I just may go with the 4 link set up. I ran into a deal a few years ago where I got a deal on eutectic CM filler rod,1/8 and 3/32, got 20 pounds for 20 bucks. The er70 would proably work just as well as you say........thanks....Rich