Bare Bones Budget 400 Build

Bighead440 said
3spds were actually standard on 340 Dusters/Darts and Road Runner/Super Bee after 1969 (IE:1970) as a way to keep the base price of 340 and 383 models under $3000 (B-body) and I think $2700 (A-body) like 1968/9 with 4spds.

On the small blocks, I knew that but not the year it became so. I had zero idea on the B/RB.
Thanks!