1973 slant six sbp or bbp?

Hi all! Got a 73 Duster that was originally a slant 6 with front disks as a donor car for my 1972 Duster. I was wondering if the slant 6 with disk was only small bolt pattern?

I read that anything 1973 and up was bbp so I picked up the parts car but it's looking like I may be wrong.

Thanks in advance!