I wouldnt worry about reusing that old handle in this bat, Its more trouble then its worth and if its the correct length now, its never going to be the right length again. i.e chasing that much missalignment you could lose the best part of 1 1/4" (as a conservative estimate). The shoulders (may have been resanded though) and width of the splice suggest to me this bat is probably made on the subcontinent for either one of their companies or for one of the western based ones who outsource to there. Ie GN, Slaz, Kook etc cut narrower 9'deg splices. Fitting a new handle would be the way to go But seeing as youve not done this before and you wouldnt be using jigs Id be hesitant to use a new handle thats been spliced to shape. The aim is to cut a kirf width outside the existing cane into clean willo, which takes care of any remaining glue residues, (+ put a "binding" cut in the shoulder to prevent it grabing)