I was recently given a rebuilt head , as part of a trade, with castings 3G21 and 87 on it. Can anyone give me any information on it? Is it an efi head?

 

I believe that there were two heads in 87. Both are efi as far as I know. I don't have the one in front of me with the casting number to tell you whether yours and mine are the same. Both heads were efi in '87 I believe. One has the 9/16" tapped holes in the exaust ports for the smog pump manifold mounted in the head aka. "air in the head" the other type does not have these holes as the smog pump manifold was to be mounted in the exaust manifold. If it was rebuilt then it should have been magnafluxed as these heads were prone to cracking if overheated. Mine had cracks in four of the six cylinders. Inspect the exaust valve seats for cracks the cracks on mine extended towards the cylinder and were fairly easy to see. Hope this helps you.
-Greg Beaman