Yes, it will be stamped YB 0611 if it was manufactured by Reinz for sale to Cosworth / Ford. If it is manufactured for sale in a Reinz packet it shouldn't have the YB0611 stamp (althought the gasket is identical). The product is the same, the package it is in is different

Reinz branded / packaged product has only been available in the last 12 months due to a contract which stopped them selling to anyone but Cosworth / Ford which has now expired.

Grov