Did you use the good manifold gaskets from Australia or the thin ones from the local parts shops? I'd personally just start with the easiest stuff first. Such as doing everything you can to make sure there isn't an external air leak. Spray soapy water on the intake and bottom of the carb near the base gasket, throttle shaft and studs. Then blow some compressed air through the pcv hose and see if you're bubbling anywhere. If you're not, then you can pretty much rule out having an external vacuum leak and then move on to some of the more difficult troubleshooting fixes.

Also, if the car is having even more trouble running when in gear. Check the points and dwell. I just had that problem with my car yesterday where I had to have the mixture screws turned out all the way to even get a semi normal idle. Turns out the points weren't opening. Fixed the points and the thing idles like a dream. So maybe just hook up your dwell meter and see what you're reading. You should be between 41 and 46*.

Just an update,I cleaned the idle air ports and idle fuel ports through the top of the carb and and it idles much better in gear now but I was able to find another 1920 that looks good and I will rebuild that one while paying more attention to the air and fuel bleeds and the econimizer plate.
I also have a 1945 that I will be rebuild to try if the 1920 dont work.
Thanks for the help
HyperValiant

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1960 Hyper-Pac Valiant(rolling test-bed)
1963 Valiant V2OO(Son's summer project,- he just turned 15 )
1972 Valiant 4dr(Daughter Kelly's repair in progress)
1974 Valiant (v8) daughter Kelly's work in progress