I've seen a lot of the Mr. Goodwrench crate engines done this way in Small Blocks, Big Blocks and the 6 cylinders also. So it may not have been as much a production or assembly line protocol as much as the over the counter protocol. But i've also seen a bunch of the crate engines with gaskets as well. GM outsourced engine assembly programs, casting foundries and machine shops to many different companies and rebuilders all over the world through the years, so it was probably just whatever that particular rebuilder had on hand at the time as part of their own personal engine building practices.
