I have an old school Bianchi Brava, ,eaning mid to late 80's
It has 105 groupo, but only 7 speed and it still works great, smooth shifting and rides sweet.
since you are looking at 105 8 speed, you could probably go with a 9 speed cassette and 9 speed sti shifters then you would have a 105 groupo thats pretty compatible to todays standards, or you could go online (ebay or somewhere0 or even get in touch with dgaddes your first replier and see what you can work out on his groupo...
Good luck to you
BTW the sti is shifters on the brake levers, sis is index or friction, I am sure I will be corrected if I am wrong on the sis, but i have always known it to be friction or index...
again good luck on your new ride