It’s a Bendix magneto from one of the Lycoming 720 series engines; it should have a part number/serial number identity plate on it somewhere. What are your plans for it? There’s nothing much you can do without the tooling/test facilities and it can’t (legally) be fitted to an aircraft unless it has the appropriate release documentation (such as a Form One stating Time Since Overhaul, Airworthiness Directives complied with, etc) I’m afraid.
It probably came off something like a QueenAir, Pawnee Brave or Aero Commander.

Thanks for the info, really helpful.