Be very careful .........2
"just carbon steel"...........not sure what you mean, but I guess you are referring to low carbon content <0.25%, frequently referred to as mild steel. It will almost certainly not be that, more likely 400+Mpa grade of medium carbon steel with alloying elements and it may not take to welding all that well. Yes, you can stick the bits together but as theresanothersteve commented this introduces all sorts of issues. HAZ in welds are significant stress concentration points, fatigue failures just love :ehand: a good stress concentration to get a start in life. Where you are considering welding, is the chassis member in tension (pulling forces), compression forces, fully reversing (both), torsion, bending, shear, the whole lot probably. Try not to weld it, have a good look at utilising existing attachments and bolt holes. Drilling holes is preferable to welding, but again, they need to be in the right place and suitable corrosion protection applied, rust never sleeps. (not my line it's from a movie [biggrin])
If you must get it welded, get it done by someone who has a clue, go find a LR approved crash repairer they may be on the right page.
Peter