Brocade fabric merge at different FOS levels

Hi

We have a customer who has brocade switches  running FOS 6.4.1a and we are looking to temporarily merge these switches with two new SN3000B switches which will be running at 7.0 FOS as part of a migration.  Has anyone merged brocade switches at different FOS levels successfully.

All switches are 24 port fully active and populated....

Thanks