Thanks. Anyone know how to convert .mpc files to mp3 or mp4

mp4 it includes video and a sound track,
to convert mp3 to mp4 is not really way to convert, just by a simple conversion
you could use a video editor creator like iMovie. there you could past your mp3 and video tracks and if you have no video you can add just pictures
other software
avs4you
microsoft movie
Premiere
finalcut
ffmpeg
if you search for video editor you may find the suitable for you