Cheers Pat,
unfortunately I am no OZ-mate, but as close as it will get, as I am from Austria (yeah the small, slightly retarded twin-brother, who communicates only via yodelling

)
Alrighty, back to topic.
There's a fine chap in the states who knocks up single inlet manifolds, he works by the name of ccworks:
http://www.ccworks.org/viewtopic.php?p=89%20-Quite honestly though, those kits look pretty sh*te, when installed.
Talking about carbs, a Mikuni HSR 40 should work pretty well, as would a big Dellorto or any other 40(ish) smoothbore. There's also a version of this manifold on which you may directly bolt on a Mikuni BST40 (stock carb on the Harley Sportster), which should be rather cheap on eBay, as all the "cool" guys in the Harley world are convinced, that they have to swap it out for something else. Same carb was also fitted onto KTM LC4 640ies...
Cheers,
Greg