Clarke Welders, which one?

[skov]

I would have thought any of those would be fine for welding the chassis.
I did mine with a very old Clarke 130TE without too much trouble.
The only time I really struggled was welding the 1mm sheet as the wire feed is absolutely rubbish at low speeds.

You'll also want a big bottle of gas and suitable regulator as those little disposable ones only give you 5 or 6 minutes of welding time