Where are you located? You state you dont know American! Are you Knowledgeable to clean and check parts? 283s can be runners! especially in lite cars like an Opel GT Etc. Your heads if they have screw in studs or pinned studs may have been reworked years ago, It doesn't hurt to clean and measure and tag, everything as you tear it down (its your labor and its free) see what you have, run numbers,You may have a jem! But if you need help and it costs money and your looking for big H. power and torque! Its the wrong choice! But you said you dont know American engines it would be a great one to learn on! And when cleaned painted and assembled should bring a better price then parting it out!
Just a thought, Jester