I have replaced the steering gear box on my 65 Mustang (Its OK, the Stang is parked next to the Chevelle). Any useful tips or techniques to get the splines on the pitman and the gear box shaft lined up. The pitman arm is still connected to the steering linkage because I couldn't get it off.

Thanks

Assuming that you started with steering wheel straight make sure it is in the center with the steering wheel straight by making an equal number of turns left and right. Then I would start it up there by hand and try to line up the splines. If it felt good and like the splines were starting I would check to make sure nothing has moved like the steering wheel position or the front tires. If all looks well take soft hammer and tap the arm further into the splines making sure it is engaged. Then double check line up and hammer it more if needed to get the nut started and torque it to the torque spec. It should go right back on. One more thing. With it on a jack check and make sure it doesn't over travel and hit the tire on something. Check both directions and spin the tires by hand. If it come back to center all should be well.