Classic/Antique Car Repair: 1987c-20 van restoration, transmission id, engine id

Question
Many and varied but to start. I need to know what is there. I have the vin but I believe the engine and trans have been changed. Where is the engine and trans number located on these specfic parts and what are the codes numbers meaning.
Thank you.
Jim

Answer
 HI James;
          ID nos. the id number can tell you where it was made and what it has in it, and other things as far as where it is , on a chevy it is on the r/f left side of the timing cover area-v-8  but on others I don't remember so I checked for you , go to ( engine ID marks  .com)  and it has all of that data. Also go to (transmission id marks ,com)as some have a lil tag held on by a bolt , this info should help you
good lock
roger