Edelbrock LD4B

I believe that if you have the early style heads, you will need a D4B. The LD4B fits later 273, 318, 340 & 360 heads.
I'm "pretty sure", but would feel better if someone could confirm.
I'd suggest posting in the "wanted" section when confirmed.

Properly tunes, a small 4 bbl will certainly make a noticeable difference.