From F/10's comparison photo's (thanks F-10) it looks like you COULD repair a broken/knackered bladed and valuable No7 bayonet by using a decent and readily available No9 blade. BUT only if you grafted/welded on an extension piece to the hilt, drilled and re-rivetted it to the No7 grip area and rear end and then made good. Worth it.....? probably not! Bit of a winter project........? Could be. Old stock No5 cross pieces seem to be available so resurrecting a No7 could be interesting but only if the donor was otherwise complete.