Ole’ Blue, my ancient road/tri bike is outfitted with 8 speed Campy Record. I’m doing the Great Floridian Half in October and want to make it a bit more “hill worthy”.
Will an 11-27 cogset work? It sure would be cheaper than going to a compact crankset and right now cheaper would be…well, gooder. 
No
Dan did an article and tried to make an 11-27 for a ten speed and it shifted poorly, 8 spd would be worse. Also you would probably need a long cage derailler for this setup. A 12-25 should be fine. I recently got an 8 spd shimano cassette and then used a wheels manufacturing conversion kit to make it Campy compatable. The cassette was $21 and I already had the kit.