I'm not an expert on these sets other than to say I like them very much and have planned on collecting the signed ones for some time. You can find a lot of them around, but of the one's that are "possible" to have been signed I would say the Ty Cobb's would have to be the hardest (if they exist) since he died in July of 61.
Here's a link to Dean's cards for the check list of the cards and some verbage.
http://1960fleer.net/
http://1961fleer.net/