The aluminum Ranier frame will need to be re-heat-treated after any welding is done to it. This will likely require repainting too. As far as the brake bosses go, you may be able to order an aluminum female end through QBP, the threaded steel part that the brake actually mounts to are fairly common but come in several different thread pitches.

As for the headset, just get to your nearest Giant dealer and tell them what you need. Depending on the bearing quality 35-55 installed is reasonable.

Andrew

www.cycle-solutions.com