you have a good comparison with your feeler guages thinking about checking head space. with your points the 19 should fit and the 20 should not fit. if the 19 will not then you would open them up more. if the 20 fit then you would have to close them some. It is basicaly the same for your go, no-go the bolt should close fully on the go, and the bolt should not close on the no-go. ...... If the bold will not close on the go, then you need to open up the space some. if the bolt closes on the no-go then you need to close up the space some. you adjust the space by moveing the barrel in or out, just like moveing that one side of the points in or out.
you say this is your first kit,,,, will you tell me what you have , is this a matching number compleat kit or is this miss matched parts. dose your trunion allready have a hole on it for the locking pin. it will be about 1/4 inch. If you have a barrel and trunion from a matching number set then must likely all you will have to do is line up the holes and head space will be ok, but still check to be safe. if they are miss matched then you will have to press and test again and again till you get it, then install the pin maby even drill a tiny bit and install an oversized pin. realy it is not that bad either way.
do not get dishartened, one step at a time it will all work out great in the end ... HAY THINK HOW EASY THE SECOND ONE WILL BE :smile: