Badass griffin, how well does a human rider fit on it?
They haven't arrived here yet, so haven't been able to check myself, but according to John, it fits just fine. Since the saddles are specifically designed for the dwarf knights, the only thing you need to do for human riders is add some greenstuff to make them sit upright.
You do have to take into account they won't be as big as GW's chickens, more in line with the old Marauder chaos griffon (so about heroic horse size).
Awesome! John is doing splendid work there. What size of base do you have that griffin sitting on?
Will the chicken-birds be cast in metal or resin?
That's a standard cavalry base in the pictures, so I reckon a 50x50 base should be ok.
Normally, they will be cast in metal.