Since your only running a 3:23 gear your not going racing and if fuel mileage is of any concern at all both of these holleys are larger than you need--so go with the smaller unit--a much better carb for the street would be an Edelbrock 750 cfm as they are trouble free carbs once you set the mixture & idle speed--the holley will shine in a car set up to race as they're very fuelish but they're not the best on a street set up--you'll always be screwing around with keeping a holley adjusted. I own 3 Hemi B-body cars & 4 big wedge B-body cars right now & build 8 to 10 each year for other guys--Ive done a lot of experimenting & this was the result of 45 years of big block Mopar experience. also if you change those rear gears to a 3:55 you'll have a very quick & fast 69--all the best to you--HemidonHi just need some of your thoughts on carb size 69 b body 440 40 over factory heads comp 509/209 cam 323 gears Should I go Holley 770 or 870 I do appreciate your thoughts.Thanks KB9GIB