were there two actors who played Blaster? *Spoilers*
*Spoilers*
If you pay close attention during the Blaster head reveal scene, you see that there isn't one long shot going from his body to his face (it's broken in two) and the shot where he's hit with arrows looks like a fake torso anyway. This leads me to believe that either his body (or his face) is just a double. This seems pretty likely as I doubt any Down's Syndrome case as severe as his would be able to cut such a chiseled physique.
But they only credit one man (Paul Larson) as Blaster. Do you think he played the body or the face? My guess is just the body as they wanted to be sensitive to the mentally handicapped actor who stepped in for just the face closeups...