I have the front end of my 1200 seam welded. It wasnt required for engineering or rego just needed to strengthen the susspension points with race susspension ect.
It would be best to actually talk to an engineer before starting any conversion is its always easier to do things with a plan of attack and saves having to redo things. I talked to my engineer several times with what I had in mind he pointed my towards and away from certain things. Different engineers expect different things too. And most importantly must comply to the ADR's on your compliance plate
Good luck Andrew