The focus mk 1 speaker may fit the hole (might need new fixing points, but should be do-able). you may be able to find one going on ebay vv cheaply too
My original speaker for my 1973 Fastback is falling to bits. I need to replace. I could fit a couple of small 12v speakers under the dashboard, but I would like to keep the original look and just replace using the one speaker on the dash. Went into Halfords and all the modern speakers were much bigger. Has anyone done this and can you recommend a speaker? Thanks.