Dating the Frame

I'm going to have to change the blog description.

So it turns out that I was very slack and just guessed that I was dealing with a 1970s frame. After visiting cykelhobby it turns out that the frame is really from the 60s! The linked page describes that frames with a serial number starting with a 3 are from the 1960s and a serial number starting with 4 is a 1970s. I have no idea exactly when and would love some help but if the brakes are original then it is most likely mid-late 60s.

Dating parts

Dating all of the components will be an ongoing process. Whilst I have no desire to make the bike truly period correct, I do want to make sure I'm within ±5 years with my replacement components. More than that though I'm just curious as to when the parts were made, what parts are original and why ebay replacements cost so much.

What I know so far.
Brakes
Mafac Dual Forge, Centre Pull.
Classic Lightweights suggest they are mid-late-60s as they are stamped "Dual Forge" and not "Racer" as the later models were.

Cranks
Sugino Mighty Competition
Everything I've read suggests these are late 70s to early 80s

...and that is it.

All comments and suggestions are welcome.