OP, please comment on why you have chosen that vintage of aluminum alloy frame to build on. Modern aluminum frames are likely far superior to those you mention in terms of both weight and comfort. All the big boys are offering up to date, shaped, hydroformed tube aluminum frames now (Trek, Giant, Specialized, Cannondale, etc.) that can be bought new, and lightly used ones should be fairly reasonable. The Caad 10 for example only weighs about 1,150 g and has a stellar reputation for comfort (relatively speaking). I doubt you can match that with something from 10-15 years ago.