i have a 75 coupe want to add electric door locks
what parts do i need ?

If you dont care that it is 100% purist stock you could use actulators from many gm cars my dad used mid 80's camaro ones on his avanti,
if you dont wanna root in the bone yard,
many parts houses like JC Whitney sell generic door lock kits giving you all the stuff you need and instructions,
cheers, T.