That Ducati 250 in Oregon might be worth keeping an eye on. It ticks most of the boxes....
* These early bevel singles are going up in price at a pretty alarming rate.
* It's cheap enough right now and most parts are freely available and not as expensive as you'd imagine.
*It's on the West Coast which makes it geographically desirable for shipping out of Sanfrancisco or
Long Beach.
*It's pre 65 legal if that's a concern.
The RT450 in South Australia seems a bit pricy but it seems to be a pretty original bike. It'll be interesting to see what it goes for (if at all). I reckon he's got 10k reserve on it.
As cool as the RT450 is, they don't come within a cooee of a B50 or even an XL350 as 4 stroke race bikes. To make one into a decent racer you'd have to do the lightweight frame thing and do a bit of serious engine work . Great Classic Dirt show off bike though.