Is there any difference with the rear suspension?

On the mef motorsport website they sell a transverse bar kit I'm assuming this is an alternative to the rear suspension arms? There also adjustable so might be worth looking into.

Does anyone know of a reputable company for seam welding? If so how much would you think they would charge. Looking to get as stiff as chassis as possible to the limit of what is possible anyway.

Cheers for the advice so far by the way very helpful