Looks to be a 1/2 bell used on either an 8ba V8 or a straight six flathead. Assuming it's for V8, if it's stamped steel is for a Mercury and if it's cast iron it's from a truck. The correct starter plate is vital for using one as they are different from other 8ba bell housings. These housings are used when installing an 8ba with an earlier trans either a top loader or side shifter trans. Can't help with how to determine if it's from a 6 or V8 other than test fit it to a block.
Bob C, does your bell take a full circle starter plate?I've got one that looks like that from a 1948 6cyl pickup.