yep ,,, i do a fair few of them too ,, 1 series scanias have been the thing of late , at least they are made from decent stuff ,, 1.2 or 1.5 , that gives you a sporting chance but a bit tougher when your beating compound curves . Oh how i dream of working in alloy , it looks like sheets of craft cheese by comparison to the stuff i get to beat about.
Last Scania I did was for someone else, it was a Scania Vabis (believe circa 1960's) and it was the grill mounting panel which was dented and corroded.
Any 3mm cutting disc will do,as i dont normally use them for cutting as such(actually,never),just the gentle grinding as stated before
And me, presuming you mean a 3" cutting disc. I did buy an electric die grinder, but it's not good for that kind of thing as there's no variable speed, and using the edge of a cutting disc to grind welds down needs a gentle touch. I also use the standard 4" one in my angle grinder - varies according to where exactly I'm trying to grind as to what tool will fit. Sometimes I use a reinforced cutting disc in a Dremel-a-like, but only for small areas.