@bnjrob Your experiences sounds very similar to mine. I also started with Urch birds but they were my problem birds. I had poor vigor, lack of egg production, low low hatch rates, and old hens. I had to introduce a new bloodline to get them back on track. I actually managed to assemble three distant lines (generations and miles apart, certainly) and crossed all three. I had/have some "interesting looking" birds as a result, but the issues I mentioned above are all but gone! Now, I can start culling hard from a much healthier pool of birds and the top birds I am raising are even looking better than what I started with. In a few generations, the throwback birds should be few and far between and I will be hauling a Tin Star (my farm) line to be proud of ... even more so than I already am!
My strategy, if I were in your shoes, would be to take the #2 best Urch cock and put him over the McGraw hens (Pen A,) then take the #1 best McGraw cock and put him over a some of the Urch hens (Pen B.) Raise as many as you can for one season, then take all the A and B pullets (they will all be 1/2 Urch and half McGraw) and put them back to the #1 best McGraw cock (or maybe the best cockerel from Pen B, if needed.) The resulting birds would be 3/4 McGraw but with a strong shake up of genes from the other line. Next, put the #1 McGraw cock back over the best 3/4 pullets. The resulting chicks would be 7/8 McGraw and I bet a pretty good line. Doing this would give you two strong lines of your own to work with.
I use the old line names for clarity, but once you start doing the selection/culling, they are no longer from that line. They are then YOUR line, built on a _______ (Urch or McGraw) foundation.
What I outlined above may be exactly what you did, I just wanted to spell it out in case someone else was interested, or you hadn't considered this approach.