Replacement instead of Vernatherm thermostats??

[Belfast Bill]

I'm having overheating problems' with my 70hp VRO Evinrude, I bought a new thermostat but the diagram showing the assembly for a vernatherm shows one cup type washer but mine has two a big one and a smaller one,the big one has the same diameter as the rubber washer that sits onto the cup, so I have fitted spring into the cup then the thermostat then the cup washer into the rubber washer and set this onto the top of the plastic cup/pot then the small cup washer then the big spring then the housing. But in the thermostat breakdown on the Crowley marine site it only shows one cup washer,I'm stuck and thing I might have blown the head gasket as the engine overheated and started blowing steam out of the pee hole,Help someone please.
Thanks Bill.