from spending a bit more time looking at pictures of carbies and the manifolds, i am confused about you statement of the carby attachment / inlet bolts being vertical, all i can find are horizontal mounts.
http://amalcarb.co.uk/other-amal-carbs/type-396-397-398.html
can you please post a few pictures here of your actual machine so we see the physical setup?
there is at least one with parts not to be found in any Howard parts manual,
see pic from Howard Register.
cheers Rod.
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