I salute you for taking on the challenge.
If it was me - and keep in mind I've never done this - I'd want to attach that jig to the chassis somehow, and probably attach the knuckle's steering link to the jig, and then re-measure everything about ten times just to be sure. Then put the pivot points on the chassis (and re-measure another ten times). Then the knuckle + pivots basically becomes a jig for the wishbones. Though I guess it might get crowded in there.