The 47050 stand is not compatible with the lathe when the extension is attached to it.
The overall length of the lathe after the bed extension is attached will be 41.1"/1044mm opposed to the maximum stand length being 31.875"/ 809.625mm, which is
significantly shorter. There will be a problem with the number of supports as well since it will require 3 supports under the lathe when the extension is attached.
To use the lathe with the extension we suggest to put the whole lathe on a long stable bench top for your safety. Attached a example which you could use as a reference
to build a larger, stable stand if you wish to (Note that the dimensions will have to be adjusted to your requirements).
Using a combination of the stand and a bench is not recommended due to lack of stability.
Rikon stand extension fits the Comet 2 bed extension: http://www.sears.com/rikon-stand-extension-70-913/p-00921097000P?sid=IDx01192011x000001&gclid=CKjunLCN1NICFdgKgQodi0IP8w&gclsrc=aw.ds