FYE on 305 E V6's, they are Big Block V6's, the E makes 165 HP @ 3800 RPM, the Bore is 4.25 and the stroke is 3.58 and the Compression ratio is 7.75 to 1. I did see a GMC BB V6 get a special intake to mount a Holley 4bbl carb but, I cannot find the site now. Your engine should be a 305E cause it replaced the 305D in 1963. Oh, I just found that site I was talking about BUT, it is a Holley 2bbl 500CFM carb on a stock manifold and get this, it was the same site I JUST GOT ALL THAT OTHER INFO FROM... Just from the GMC V6 engine Performance upgrades section instead of engine specifications section. Here it is http://www.6066gmctrucks.org/performance.htm it's recomended for performance upgrade on these motors, it's the only performance upgrade I know of for these old GMC BB V6's