Unfortunately the chart compilers are fairly strict about people creating chart archive sites and usually force them to take down the info. I don't know of any site that has charts from the mid 80s (although by visiting various newsgroups you can pull together the top 40 from 1973-84 and 1992-7, mainly at uk.music.misc and rec.music.misc). There is a book, now out of print, called Top 40 Charts which has all top 40 charts from 1960-95 and your local reference library should hold a copy.
