if the battery tests good a length of wire and jump the connection from the battery to the starter directly. It will either try to crank or it won't. If it does it's a connection - hell I will gladly swing by after 5 if ya'll would like and see what I can find or help with. 5 "blocks" isn't that far for me to go. And 2 heads and an extra set of hands never hurts.
This too is what I would try next if the battery is good. You can basically use a set of jumper cables and route them to the starter just like the battery/starter cables are ran ( this will eliminate the possibilty of a bad positive or negative cable ) Its a little bit of a tight fit so be carefull routing the jumper leads down there and make sure you get it on the right terminal or the starter could engage. GM side post batteries seem to be worse at hiding corrosion and that corrosion can travel down the cable ruining it too.