DIY 4-component Buck converter, no ICs, need help with maths

I'm building a bike light around a Seoul P4 LED and some re-purposed 18650 li-ion cells from a laptop battery.

I'll need 700mA constant current and can comfortably fit 8 cells in my enclosure.

I've done some reading and I should be able to build a Buck converter relatively easily, but I'm struggling to find any good guides to help me spec the components. I asked on Dave Jones's EEVBlog forums and all the replies recommended either Linear Regulators (wasteful) or something designed using Webbench, which only helps with circuits featuring ICs.

As a buck should in theory only need a transistor, a diode, an incuctor and a capacitor I want to build it myself out of through-hole components.

Can anyone help with some guides or tutorials on specifying these components please? My degree was Computer Science and I was definitely better at set theory and boolean algebra than anything involving formulae!

Switchers are not for amateurs - I'm a pro, and I wouldn't design one from scratch. National's simple Switchers are by far the fastest, most robust and easiest way to do it.