Been a while since I was here due to being retired and doing very little these days but was presented with a question that I can't answer:

We were given an older generator that has an L6-30 receptacle (3 wire) built in and is labelled 'Neutral Bonded to Frame'. The frame has a lug for a rod. The cable we currently feed this small building with has L14-30 on both ends (4 wire). Can I get an adapter that will plug into the L6-30 on the machine and give us an L14-30 Female so we can use our standard cable? It feeds a small panel in the building that has 6 circuits that have nothing but one GFCI receptacle on each. (Neutral and ground separated in the panel & a permanent rod outside the building). No multiwire circuits. Separate line, neutral and ground to each GFCI.
This building is seldom used and currently we roll out a 7500 Generac (also labelled 'Neutral bonded to frame'), attach the geny frame to a rod that is already in the ground and use a standard RV cable (4 wire) since this unit has the L14-30 (4 wire) receptacle on it.

It seems to me there should be no issues but I am, by no means, a generator expert .... which is why I'm asking you guys.

I see no issues with your proposal, though I would, when I roll it out, connect it to a readily available grounding electrode system that I would put in just for this building. I am assuming that there is no power at the building except when the generator is wheeled out.

I have the same question as Mr Brown. Is this a backup and if so what does your transfer equipment look like? Does it switch the neutral?
The generator is set up as an SDS so it will need a compliant ground electrode system. (probably 2 rods)
As a practical question I doubt this is a safety issue as long as you have assured the generator really has the main bonding jumper installed and the GES in the building is good.

There is no xfer system. There is no permanent power. We roll out a geny & hook it to the inlet. There is no power unless we hook up the geny. The ground rod system is permanent. We simply unhook the wire when we remove the generator.

If you have a grounding electrode at the generator this is a compliant SDS. Going to the 4 wire feeder is legal from that point. If you also have a grounding electrode in the disconnect enclosure at the building that makes the whole deal compliant. That can be the same electrode system if these are all grouped together.

IMHO