I recently completed a volunteer redesign project for a local non-profit pet adoption center. Before doing the redesign I found that their old webmaster had put tons of hidden text at the bottom of every page, unbeknownst to the owners of the adoption center.

Now the redesign is complete and none of the new pages have spam. I see that the old pages still show up on google though. I'd like to 301 redirect them to their appropriate replacements, but I don't want to transfer any "negative opinions" google may have of those spammy pages over to the new pages. I could simply delete the spammy pages but then they'll give 404 errors to anyone who legitimately lands on them.

Anyone have any thoughts on what the best way is to handle the situation?

Meanwhile, the site shows up well in google for their terms, so if there's been a penalty it's not extremely obvious to me. I signed up for webmaster tools and there are no notifications about problems with the site. So maybe they flew under the radar, I don't know.

Thanks in advance!