a 289 cant be bored to a 302
a .030 289 is a 293
a .060 289 is a 297
but thats not really your question anyway...
there is no answer for your question based on the information provided : (
there is a formula that will give you a ball park answer but its not real accurate, it has to do with c.i.d. and rpm
to make a good carb decission you need to decide on what camshaft you are going to be running and what your heads will flow
it all has to work together or you will lose a lot of potential horsepower
for a low horsepower mild car a 600 vac sec is a good choice
for more wild applications(6000+ rpm) go to a mechanical secondary and maybe step up to a 650 dp
in almost ALL cases a 650 dp is plenty of carb for a 300 inch motor
my old motor spun 7500+ rpm and had heads that flowed well over 225cfm in. with this combo, The Carb Shop, in ontario ca, set me up with a stage 3 650 dp which is what i recomend to everyone, have a pro set you up
The formula is: Cubic inches X Max Rpm divided by 3456 = CFM. One other thing that comes into play is your VE...Volumetric Efficiency. Most stock motors have a VE of about 75%, so you then need to multiply the answer by 75%. High end race motors may achgieve 100%, and the VE will also vary accross the rpm band.