I always install the disconnector, sear, hammer, grip safety, and safety, to hold the grip safety in place, but leave the safety off, FIRST. That is a good way to check them to make sure you have everything in alignment with nothing out of whack, with just finger pressure instead of spring pressure....by pushing on the hammer, you can pull the trigger and the sear should release the hammer.
Then if I remember right (to be honest, I have done it so many times I don't pay attention anymore!
) I leave the hammer DOWN, (uncocked) so the hammer mainspring strut puts less pressure on the mainspring when you install it.
Make sure the sear spring is in the right position (my AMT frame has two cuts for the sear spring, about 1/16" or maybe LESS apart, and I ALWAYS end up with it in the WRONG one the first time, and have to take it apart and move it
) then I kind of hold the frame in my hand while sliding the mainspring housing into the channel, and when the housing contacts the sear spring, to hold it in place, I kind of jiggle and move the frame around (if you don't use a vise, this is one operation where a third hand would be handy!) (I USUALLY end up with the frame verticle, so the strut is kind of "hanging" like a pendulum,) until the strut is centered on the cup at the end of the mainspring inside the housing, and the grip safety is in the proper position, put a LITTLE more pressure up on the housing to hold the strut in place on the cup, then still holding it firmly in place, I push the frame DOWN with the mainspring housing on a block of wood until it is in place and I can stick the pin in with my free hand.
My mainspring housing has a lanyard ring which makes this easier. as I press the ring on the block and it's easy to line up the pin, but I've done it with a flat bottom one too, you just use the edge of the housing to press on.
You can also do it with the frame in a vise, and use a small screwdriver or punch to position the hammer strut centered on the cup, and press against the mainspring housing with a brass punch or wood dowel, but I think it's easier my way, ESPECIALLY since when I get it together it DOESN'T WORK since I put the sear spring in the WRONG SLOT
so I have to take it apart and do it AGAIN!
And after swearing at myself, I do it RIGHT, it WORKS, I'm HAPPY, until I think AGAIN "WHY DIDN'T YOU MARK THE RIGHT SLOT, IDIOT!
" (Believe it or not this conversation with myself on reassembly has happened for OVER twenty years!
And yeah, I remember now, because the FIRST test I do then is COCK it, so yes, you install it with the hammer DOWN, at least I do....
Just make sure you dop not actually drop the hammer by pulling the trigger and letting it fall unsupported when it's apart, it can bugger up the hammer/sear....always "catch" the hammer with your thumb on it to check whether the trigger works....