Well, I guess one "can" build a motorbike ... from "fleabay" parts.
I started with 1969 650 motor, and a seat. Pretty much everything else from fleabay over the time. Took about two years of gathering additional parts and fiddle farting around, working on it when I felt like it. Nice to have it finally finished, and its fun to ride.
Has a 1976 T140 frame, 1969 Triumph T120 engine (complete rebuild with all new bearings, seals, gaskets, and crank sludge tube cleaned.) Disc brake front end, etc, etc.
I don't even want to think about how much I spent.
I used a Nissin M/C for the front brake with built in stop switch, and a single stainless brake hose with adapter fittings. I think it is a much neater and cleaner install than the stock setup, what with multiple hoses and pipes, and all the junctions just waiting to leak.