what size carb

Here's the best intake for that engine as long as it's a 66 and later model (the 64 and 65 engines have different intake bolt size and angle). The ld4b is great on a stock or slightly modified 273 or 318. I don't know why someone hasn't snatched this up yet...

http://www.forabodiesonly.com/mopar/showthread.php?t=323010