pigtailed aluminum replacing regular receptacle to GFI
Almost everything in mains is done in hot-neutral pairs.  GFCIs are no exception. LINE has 2 terminals, brass and silver, and is used by a hot/neutral pair - both black and white wires go to it. These would be your two pigtails. 

LOAD is used not at all, unless you intend to use the particular feature it supports, and you know exactly what you're doing.  That's why it has warning tape on it.   You do not seem to know what that feature is, which is fine; simply don't use it. 

Use an AFCI+GFCI breaker instead

Some people say install a GFCI breaker which protects the whole circuit.  It's true, it'll be cheaper than GFCI receptacles at every socket or 4 alumiconns for doing it in this box.  but think bigger. 

Arc Fault protection (AFCI) is absolutely perfect for protecting aluminum wiring.  It detects the thing that is most worrisome.  AFCI has to be installed at the breaker because it protects the wires.  

They make combination AFCI+GFCI breakers that cost only $10 more than a GFCI breaker.  That is the thing to use.