welding milodon sump. Mig or Tig?

I have to modify my sump to clear the steering rack and was wondering if welding it with my Mig will be ok or should i get it Tig welded?
The plan is to cut a 35mm band form the walls and lift the whole floor of the rear section up then use a section of the offcut to patch the hole. It will end up being approximately 1mm from the windage tray which i think i will have flatten it off slightly to get more clearance.
Can anyone see a problem with this?
Thanks in advance,your input is appreciated.