It is possible that Stinky will purr once he starts feeling more at ease around the home. As you said, he wasn't in great condition when you adopted him so he probably didn't feel as ease in his last "home." If he was only used for stud he quite probably didn't have the interaction he needed to become comfortable around humans. Give him time.
I was talking to a person who used to live in my area through my work a while back. She had a Bengal who dissappeared one day. Funny, she told me he was fixed. But my ferals are showing up with very distinct red colouring...
Assumptions do nothing but make an ass out of u and me.
We can stick our heads in the sand for only so long before it starts choking us. Face it folks. The pet population is bad ALL OVER THE WORLD!