nothing much to add here from me!

block it, leave it open...it's your choice.

to help you decide--some theory behind it! the reason it was there originally, was because these cars were driven year round...or at least, engineered to drive year round. that's why the carbs have chokes, the exhaust has those little flapper valves and the intakes are heated with exhaust gasses. the passenger side "flapper valve" thingy was shut when the engine was cold. this blocked the exhaust (not entirely though) and made it go through that port, through the intake, and out the driver side exhaust. this was to heat up the intake, and to help the fuel atomize, or stay atomized as it passed through the intake, as well as simply warm it up to make it easier to burn. as the engine warmed up, your choke would open up from engine heat, and that flapper valve would also open up, allowing the exhaust an easier shot at going out instead of through the cross over (but, some will still go through it even at full operating temps)

today's cars are usually NOT driven year round, and some semblance of performance is desired from them. for maximum performance you want a free flowing exhaust, free flowing intake, and a COLD air/fuel mix coming into the engine because colder air is more dense, and has more O2 to burn, making more power...thats why Cold Air Intakes are so popular...even if they only provide you with 2 or 3 hp. (they all advertise 15-20 though! some do, some dont!)

so...ask yourself, is this a summer only vehicle? or will it be used year round?

mine is a summer only toy, so my cross over is blocked, and the exhaust is free from any "flapper valve" (sorry, I don't know what it was actually called), and my Carb does NOT have a choke. It really doesn't like to start when it's 45 degrees or less outside, and even when it's 85, I gotta sit there and hold it at 1500-2000 rpms for a few minutes until it warms up enough to idle without stalling.

but once warmed up, it idles great, and hot starts are NEVER a problem.

now you have the information to make the decision on your own, instead of just counting up how many people have said "I have mine open" compared to how many said "I have mine closed"