What is a most suitable size/material for a big SMPS transformer ?

[Refrigerator]

Hey.
So after my first attempt at building a welder i completely and utterly failed  . The welder can barely sustain an arc and won't even weld. So i saw this inverter welder schematic ( over here http://all.chury721.cz/WEBY/www.danyk.wz.cz/svar_en.html ) and i thought i'd give it a try. It looks simple and easy to build yet i'm not too sure about the transformer part of it.
I don't have any big ferrite cores for a transformer but i have plenty silicon-iron sheets, plates and transformer cores of different sizes.
I've torn apart a PC power supply and it had a silicon-iron core transformer in it, so i guess it is possible to do it.
What i think of using is a small toroidal core from some rather unusual looking device.
The dimensions are 25mm x 68mm x 40mm ( H x OD x ID );
Here's a photo.

I'd like to ask if it is possible to make a decent size SMPS transformer with silicon-iron as a core.
Or do i just wind it like ir says in the schematic and hope for it to work ?

[JohnnyBerg]

You cannot replace ferrite with silicon-iron cores.

As for the core, there are many distinctive factors. The 2 most important are form factor (like E, ET, Toroid) etc. and ferrite material. Yes, there are more different ferrites, then the colors of my wife's hair.

Before making any attempt on building an SMPS, I would suggest you get familiar with the most basics of SMPS. Its not something you build with thorough knowledge of the do's and don'ts.