A 283 is a V-8 but not being a Chevy guy I'm not sure what a '50 inline 6 was, a 235 maybe.

There are lots of suppliers for Chevy patch/repair panels. Here's just one:
http://www.rustrepair.com/app2/onlinecat.htm?p=sm

Rust.....cut it out and weld new in, don't cover it up with Bondo or it will be back again.