If you look up a 1957 electric start model RJE you will see just before they list the Arco replacement starter you refer to #5376 there is a kit #175019 which is a starter & bracket assy. This is on MarineEngine.com. You will need that bracket to hold the smaller starters of today. Not saying you can’t find one on eBay or at a meet. You might try "Free Advertise" on our site? They are out there.

Dan in TN