The bolts will work fine, so welding is not necessary, unless very thin metal plate is used.
Then a tig welder would be a better option than using an arc welder. It is very easy to burn holes in the thin metal or end up with a bad weld if the wrong arc setting is used.
Just ensure that you use countersink type bolts / metal screws, to keep the underside of the stand as flush with the aluminium as possible. Also use loctite the lock nuts or use else use nyloc nuts to keep things together.
You may want to trim back / grind off any excess bolt thread sticking out above the nuts, to limit any grass etc from attaching itself to the enlarged footprint when riding off pavement. The lower the lock nut profile the better.
I made use of a PVC cutting board to make a larger kick stand foot print for the XT500.
As a matter of interest, by how much have you increased the foot print?
Does new footprint clear the centrestand when both are in the rest position?
