Yes, the medieval bull looks great. You mean industrial?
If that's the case, the industrial sitting bull head you planned on using (page 4 of this thread) looked fine, with the beige shirt and no feathers, etc. But if possible I suggest removing the pony tails in the industrial, to distinguish it from the other ages a bit.
Modern age is tricky, I searched but couldn't find any helpful clothing or potential prop ideas. I hate the idea of just westernizing every leader head for the modern age by just giving them a suit, but I guess what you had for modern would work for lack of a more unique idea. Could you deform the collar on his shirt and jacket though? Make it look a little less plastic-y. The modern backround you selected looks good; indian looking, and resembling a casino.
What you have so far looks great. I really hope you complete it.