The 45-70s you have been seeing are from back in the 90's I believe. Davidson's had a run of 5 special 1895's made for them and two of them had half octagon barrels. The only other one was produced in 1995 as a 100 year commemorative. They called it the Century Limited.
Anyway, to answer you question, no, there were no half octagons built on the 336 receiver in 30-30. There were only four models ever built with a full octagon barrel.
There were 30-30s built with half octagon barrels but you would have to go all the way back to the Model 1893.
-Bob