L6-30 to L14-30

We have an older generator that has an L6-30 receptacle (3 wire) built in and is labelled 'Neutral Bonded to Frame' The cable we feed the small building with has L14-30 on both ends (4 wire). Can I get an adapter that will plug into the L6-30 and give us an L14-30 Female so we can use our standard cable? It feeds a panel in a small building that has about 5 circuits that have GFCI receptacles on them.