Another thing to note about welding a pitman arm is that it is cast steel. While it is a similer material the cristlan stricture (?SP?) is different and therefore the origional cast material will have different expansion rates when heated. The problem with this is than when the weld and cast portions of your part cool they will shrink at different rates and want to develope cracks.

The easyest way to prevent cracks is to pre and post heat the part with a tourch. Then force the part to cool very slowly. I usualy wrap parts with some scrap foil lined firewall insulation and then pile on a bunch of closed cell foam.