If it's any help the Truvativ Touro crank set on my SCR4 '08 were 170mm, measure ctc i.e. centre of the hole that the crank bolt goes in , to the centre of the hole where the pedal axle goes, not sure which crank set the scr3 has, but as the frame is exactly the same, as are the wheels Alex 22's then in all liklehood the Tiagra? cranks will still be 170mm.
When I put the Campy Veloce cranks on at 172.5 I did suffer with a bit of toe overlap, just something you need to BIM when changing cranks