Usually a good idea to jet it stock and then tune from there. Since you are planning on using a 2 -> 1 adapter rather than using a two-barrel intake, I would highly suggest initial plugging of the power system to dial in the main metering jets. The two into one really messes with the vacuum signal.
Just guessing, I would say that with no modifications, it will be pig rich at cruise and very lean at WOT due to the two into one, plus the idle will be exceptionally lean. Believe you will need to eventually use a different power valve actuating valve spring to keep the power valve from being open all of the time, richen the jets 3~4 sizes (again, screwy vacuum signal), and richen the idle jets 0.003~0.006 inch (vacuum). But don't do any of this unless you need to. Just believe this is where you will end up.
Oh, and the vacuum signal to which I refer is the negative pressure in the fuel wells of the carb, not the engine vacuum. The fuel well negative pressure is controlled by air velocity, which is effectively killed by the 2 into 1.
A much better situation would be to modify the original manifold with a two-barrel plenum and NOT use the adapter. Results will be MUCH better.....driveability, power, and fuel economy.
If you watch NASCAR, think "restricter plate"!
Did a LOT of testing one to two and two to one years ago; NEVER with positive results. Average was the two-barrel would produce about 75 percent as much power as the single barrel it replaced.
Jon.
