Dirk,
The books by John P. Stewart were given to me several years ago, so I'm not sure where they came from. There is an address:
Copywrite 1981 by John P. Stewart, 233 Dupras Ave., LaSalle, Quebec, Canada, H8R 3S4 Tel:(514)366-8410 Fax:(514)366-6358
Tenth Printing Jan. 1996
If you can't find these books, don't sweat it, there are lots of other good books on the subject. Several were listed in other posts. I'm just partial to what I'm familiar with. The guy has written the book in language that I can understand and it just makes sense. Nothing can make up for actual experience in straightening distorted pieces. After you have had to wrestle with a piece to get it to move with heat in the direction you wanted you'll learn what to do and not do. Remember to use your temp. sticks to keep a check on your heat to keep from over heating your piece. For mild steel I use 1100F temp. sticks to help monitor the heat(at 1200F the steel will cripple). Around the place you need to add heat, take the temp. stick and draw a circle around the spot you plan to heat. When the marks you made with the temp. stick melts, you have reached that temp., stop heating and move to another spot. Practice makes better(not perfect because steel is not perfect).
Get out there and practice! If you only get weld on one side, you will have to heat the other side to get it back straight.
John Wright