These engines were discussed not so long ago in another posting listed below.

https://www.stovebolt.com/ubbthread...amp;Words=265&Search=true#Post636135

In 1957 283's were available with any transmission option. The 1957 283's did not have the side engine mount bosses, and only had the front engine mount bosses. They are highly sought after engine blocks too. Probably because of all the popular 1957 Belair and Nomad/Delivery restorations.