Here is one, I made it myself.
http://www.thestalkingdirectory.co....ble-mag’-conversion-for-a-Howa?highlight=Howa
ATB
Tahr
ejg/ Techno B
Not claiming certainty from the Weatherby site picture, but that system ( aside from mag capacity / lengthy ) looks to be near identical to the Howa supplied Short action one.
ejg - was yours packaged Legacy or ATI by any chance?