340 buildup advice

If you run hydraulic cam, I recommend using around 284° duration. Then throw in a set of Rhoades variable duration lifters to tame out the idle and still have full top end.

As for carbs. If you use 4 bbl or 6 pack, install the yellow spring for the vacuum advance so the secondaries open up faster. That is the trick to getting a 6 pak to run. A 6 pak is not that hard to tune, you just got to get in the mindset that they are just like a 4 bbl but with 2 sets of secondaries.

I run a 340 in my Formula S with the MP 484-284 cam and it has a nice idle. It is a little rough at idle and idles at 1100 rpm. Then you have to recurve the distributor to get it to run properly. It has 3.91 gears and runs 3000 rpm at 75 mph.