The data you want are from the 2000 Census. It had a long form, so those data would be there. I am pretty sure they classified low/moderate income in 2000. I would go back to HUDUSER and look.
It has to do with the Area Median Income, which is complexly determined based on household size. I know these sorts of data existed in 2000, because we used them in a case in Westchester. Hope this helps.