Hi Yes I split the vent line for double duty as the pulse and still vents, seem to work fine. I figured the area of the glow carb and the WT-499 although larger seem to fit the bill ok, A person might can go a tad smaller throat Dia and still have good Top RPM's, you need to remember your only feeding an 80 size engine per stroke, or even a carb with a accelerator pump I am told works good. I myself didn't see the need of it but some do.
The manifold was not hard to do with the help of a lthe and milling machine, you can see if the pics I turned the exsisting manifold 90 degrees and made a retsiner to rebolt things back into place to hold it all together.