In the link http://www.pbm.com/~lindahl/ballads/
One mention is of Bruce Olson's 'website', which is now hosted here at Mudcat. You can find it at 'quick links' at the top or at:
https://mudcat.org/olson/viewpage.cfm

Many interesting and arcane items from his years of research. His Mudcat posts are still available with a search.