thanks

As far as I'm concerned it's now finished, I've completed what I wanted to create. Latest and (currently) last addition to the tool is an Addborders(0,0,0,0) AviSynth type output for directly putting into an AviSynth script or using with whatever other tool you're using to expand the footage up to full PAL/NTSC/HD resolution.
Along with being able to put 4:3 footage into anamorphic by adding side borders instead of zooming in and cropping the top/bottom.

Before I set out to write this I had a look round and was surprised there weren't any tools that did this exact task, most were just concerned with the basic 4:3, 16:9 & 2.35:1 ratios and weren't flexible enough with the source x,y values.