the only specs involved would be the offset of the secondary and the center to center of the cutches.
yours should be same as most and set at apprx. 15mm (9/16)for the offset and 268.5mm (10 9/16) for the centers.
problem with using makeshift tools is fitting them between the primary and the bulkhead, but it can be done. make sure they are straight.
what you are trying to achieve is that the clutches are running the same plane. if you improvise a straight edge, its best to get one long enough to touch or span all the way across both clutches. you can get relatively close with this method, even close enough to probably never have any belt issues.
the difficult part is maintaining plane and center to center when tightening down the mount bolts. trial, error, and patience will save you from buying $50 worth of tools.