Marty Feldman as Yoda, yes, yes and yes. Couldn't find any mockups but he did play Gollum apparently...

also, Scatman Crothers as Mace Windu (Scatman breaksdown and cries when Lucas makes him do 40 takes of Mace telling Anakin he will not be trained):

Joe Turkel as Grand Moff Tarkin:

Tarking blows up Alderaan...

Leia - "And you call yourselves Human?"

Tarkin "'More human than human' is our motto"

LMAO

and Shelley Duvall as Princess Leia (This would have been genuinely awesome IMO):

(See what I did there)