I cold set my 72 Moto Grand Record with the 2x4 method and no clamp, and it went fine. I spread it to 128mm so I could use a 126mm wheel and move to a 130mm wheel later if I wanted to. Little moves, check it constantly...

Mine has the last remnant of a decal with a "3" on it, so it is definitely Reynolds main tubes only, not chainstays or seatstays.