Here are some really great links with a lot of information about the show.
https://marthawilliamson.com
On the front page of her site, there is a tribute video to Della Reese.
https://marthawilliamson.com/video/musical-tribute-della-reese/
The Touched By An Angel portion of her website:
https://marthawilliamson.com/touched-by-an-angel/
And this is a photo of her and Della:
Next is a site that is about John Dye. This one is in Italian, but there is an English version as well.
http://www.johntheitaliansite.com/
Lastly, here is another John related site.
http://www.payitforwardinmemoryofjohndye.net/