L6-20P -> L6-30R

I have a situation where a 208v/20A PDU (L6-20P) is supposedly hooked to a 208v/30A circuit (L6-30R). Before I order the correct PDU's and whip cords...sanity check...are connectors 'similar' enough that this is possible (with force) or am I going to find we've actually got L6-20R's on the provider side? -- ~Randy