O.K. I finished the Pitman arm mod. I did a lot of research, and talked to a few professional welders and they all said the same thing about welding on forged steel. You have to heat it up to between 400 and 500 degrees before you weld it, and then you have to cool it down in stages over a long period of time.
I took the pitman arm to my buddies machine shop and had him bore the tapered end out to 3/4 inch with his end mill nice and slow. I also had him do a scrap piece of 2" x 1/4" flat bar, so I could make the top piece.
I have a gas oven and I preheated it to 450. While it was preheating I tacked all the pieces together.
I then put the arm in the oven and left it for two hours. I pulled it out and ran outside with it and welded it up. Of course I didn't weld it with the heim joint in there.
I then ran it back in the oven and baked it at 450 for another hour, then I turned it down 50 degrees every hour after that untill it was at zero. I left it in the oven the rest of the night without opening the door so it would cool down to room temp as slow as possible.
The next morning I took it out and tried fitting the heim joint back in there and it had shrunk down just a bit, just enough. So I mounted it in my vise, and broke out the trusty old Nicholson file and "messaged" it just a bit on the pitman side, until I had a slip fit with a little tension.