I have found the two-piece manifold to be the underdog of the twins. Nobody liked them, simply because you had to re-seal them occasionally. So what, they were more efficient than the big iron log.
There ARE single piece cast aluminum out there, if you are just wanting to save weight...
As far as an external vent, drill and tap just under the air cleaner surface for a small barbed brass fitting, you can find them on RC car websites, or ebay. be sure to have a short hose and filter to the vent. These carbs HATE contamination. Do not use a rock-style filter, as there is too much resistance, and won't vent properly.
Where to drill? You'll have to look at the casting to determine that yourself.
