I was pretty sure there are staggered bolt 283's. I'll see if I can find the numbers under the #2 plug tonight.

I know it has the firing order on front of the intake, but there is also a casting number at the rear of it, that is what I was reffering to.

Most of these linked sites don't go back to the 50's.

I got the complete number off the front of the block, it's TI 223 D