What I heard (so far) is that you need to buy an XR conversion (+11mm rear motor layout), and then an XM conversion to convert the XR car to the XM spec... so it may well be more expensive than a Vega conversion
The XM is the car Lee used at the Worlds warm-up. At the actual Worlds he used a different spec - there is a topic in the subforum where Lee mentioned the situation (
link).
So if you're looking at Tamiya particularly, you might want to wait for a bit - I know Tamiya was a bit untactical with the upgrade sets and conversions with the TRF511...
...However, being the runner ups in 2WD at the Worlds I can imagine they might be working on the XM as a kit and with moulded sidepods, gearbox and shock tower. They've butchered the original car so much by now that it's time for a new kit - if they want to get those extra sales from their result at the Worlds, that is. If that will actually happen only time will tell
