gt40p head question

Does not matter, each head is identical.

Look at the threaded holes on the ends of the heads. One end may have threaded inserts in them. This is for the accessories and needs to be in the front. Your heads may not have them, which means you will need to take them out of your stock heads and swap them in.

That's about the only side-specific part to them. I once slaped some E7's back on a motor after doing HG's only to discover the accessory threaded inserts were at the rear of the motor