RGsB Converter

I have an old system called Vistagraphics made by a company called Calcomp.

It outputs a signal to a monitor via three 75ohm BNC connectors.

The sync signals are on green.

(I think this is known as component)

I want to be able to capture the image and print it.

My thought was to convert the signal to either s-video (Think this is also known as composite)or VGA.

I have not been able to measure the sync pulse, but the thinking is that the signal will be in the region of 15khz wheras a modern VGA monitor uses around 31khz.

I would preferably like to build my own converter.

Does anyone have a design that works ?

There is an IC called an EL8102 made by intersill that strips the sync off green, but then I have no sync signal ?

I would also somehow need to re-sync the picture and alter the frequency to work with VGA.

Failing that does anyone know of a cheap premade product (preferably UK sourced) that will do the trick.