I'm not a Macwester expert (and they did seem to use lots of names for boats with only very minor differences) but I can't find any trace of this one. Are you sure you don't mean a Marcon Claymore?
I would agree with Silkie, I think you mean the Claymore built by Marine Construction Ltd in Southampton in the 70's.
I have a scanned copy of the Builder's catalogue from about the mid-70's - if you PM me an email address I will send you a copy, no worries.