Never used swingarm extenders from Cognito Moto. Designed for a CB350. $45.00 shipped obo.
https://cognitomoto.com/products/cb350-weld-on-swing-arm-extenders
IMG_20180105_201655 by J L, on Flickr
https://cognitomoto.com/products/cb350-weld-on-swing-arm-extenders
IMG_20180105_201655 by J L, on Flickr