If the primary applicant is not yet done with his Stamping part for the Extension- but he is having the valid Conversion pettition til 2014 also he is having the hardcopy of the pettition
It should be fine to go for stamping. Just make sure the person has all the required documents. These days, do not treat H-4 visa stamping any easier than H-1 visa stamping. So I suggest taking all H-1 employment documents as well when going for stamping.