Ok, so when i was building my engine one problem i came across was the supercharger drive belt was weaving left to right. after stripping the crank pulley and measuring float many times which was correct, i was sure that the crank pulley was true. so next i checked the actual pulley on the supercharger pulley which was true, but the belt was still weaving. It turns out the tensioner pulley in the "Ebay" fitting kit i got was around 4-5 degrees out and this was the issue. after looking around in the unit i found a timing belt tensioner on a scrap iveco daily engine which after boring one of the holes a millimeter larger was a straight fit.
Once fitted and tensioned up it now runs true and i'm no longer destroying belts.
I hope this post helps somebody else, and saves you the time that i could have saved if i knew before hand.