Thank you Lorsar
I have just sent off for a sample of that Martrim..
Meanwhile, with the most gracious help from JamesL in supplying templates, I have managed to use project card(£5 a sheet) to complete what I think is neat job for now..
Even managed to fit my second(useless) speaker in.. not,I fear, for the purists..
But, until I get the right card, it will do as an trial fit…