Question about buying Carter BBD for my 318 (unless I should look at something else)

Demonracer said
It's a tried and true combination, I've run that set up on 273's, 318's and mild 340's. I almost 99.99% of the cases, the fuel economy was better than any 2 bbl on the market. You will see no difference at a cruising speed at 2500 and under. You will see more and better performance when you plant your foot in it.

Looking at Edelbrock's website, I'm not able to locate a "635 cfm" carb. I see various carbs in the 600 to 650 CFM range, with prices that range from $400 to $500.

$450 (USD) is $600 (CAD) for me. I'll add $200 for a suitable intake manifold, gaskets, etc. With tax that would probably bring me to $900 (CAD) total.

Just pulling numbers out of the air, if I saw an increase from 15 MPG to 20 MPG with the new carb, and if I drove the car 2000 miles a year (which would be quite a change from driving it zero miles in the past 25 years), the payback would take 4.5 years.

Is a 33% improvement in MPG realistic? Is 2000 miles a year realistic? Obviously this is not my daily driver (I probably drive less than 5k miles a year as it is).

So no, I don't think that spending $500 to $1k on a carb/manifold like that is in the cards. Putting half to a quarter of that money towards electronic ignition is more likely.