And then there was one les

The best thing you can do is go back to where you got the script from and ask there. They are the best person to work with it, There have been some changes to the templates in different versions so just because it works on one version doesnt mean its going to work on another.

inside orderforms/complete.tpl You will see an ispaid switch. Using that you can add in your own custom workings or simply rewrite the whole template to meet your own ends.