sboardcrazy said...Just out of interest, are the ones you bought on the boardcrazy website?Yep.Mystic Harness Line Set Pro Vario
Boom diameter is 40mm..I just assumed that modern booms were narrower as a few Id seen were.Maybe I'm doing something stupid with the way i have them on..

Wow, I thought 32mm was big. I guess you are right, 40mm must be too big for modern harness lines. I have noticed on some of the harness lines I have that they are a tight fit, and that's on a 32mm boom.
It is still interesting that you can't attach them. From the photo they look like typical lines in that they have a loop that goes around the boom and the velcro should only be for tightening them up. Without it they should still carry your weight no problem.
Oh well, you might have to go get a more modern boom. Not a bad problem to have in the end.