What do i have?

You may find an IH "Binder" mark cast on that block somewhere. IH cast some 318s for chrysler in a short partnership during the (I'm thinking) mid to late seventies for the industrial/marine line. Clean the front of the block below the drivers side cylinder head to see if any numbers are stamped in. But I can't say I've ever seen a 318 transplanted into one of these, yet!