I was attempting to work this one out yesterday, and couldn't get it to make sense either. It can't be "joyful and happy men" because both iucundi and felicis are genitive singular, right? So if they are substantive it will have to be "a joyful and happy man".
I'm leaning towards:
"yet the life of that (one) retains something of a contented, pleasant, and happy way"
(I don't even know if what I'm trying to do is feasible ;)