Hi,
earlier carbs will fit fine, but you are best off getting the originals cleaned professionally. ( I had mine done a few years back for £50 ). The earlier carbs may look clean but unless you know where there coming from you cant guarantee they'll be any better than the present ones. If you do them yourself immerse the innards in nail varnish remover or paint stripper-you can re-use the gaskets.
Hope this is of some use
Cheers