couple of things to throw in for you....
ive done tons of 9" builds with no guide rod and no problem.
its all about the cycle distance and keeping it all on track. if the stroke is long enough to get the round on the boltface while keeping the piston in the FSB housing??
then you dont need a guide rod.
ive never done 7" builds..
my builds go from 9" and drop right to 5" & then 3" & 1"
but there are several different set up s for this & yes you could use a denial bar style set up in the top cover to keep it all in line.
only reason i never went this route was the covers are so thin and they have a lot of variance in them in there with the spring wanting to ride up and so on..
when i drill the gas block from the front i actually do it with the piston on the carrier and a dummy round locked into the barrel..
so it IS where its gonna be. this is the poor mans way of guaranteeing your alignment.
lots of your super machinists will measure and measure and measure.... but all you really need to do is have it where its gonna be and then keep the holes tight.