Don't weld tow bars or hitches unless qualified - Tow bars and hitches come in many heights and types - check on line - I note you are in Perth and found this local guy www.metrotowbars.com.au/ or contact your local Pedders.

For this type of welding you need someone who is a coded welder not just some backyard bloke who thinks he can wave a torch around. It would also be prudent to have a Dept of Transport approved engineer to look at what you are proposing A list of those can be found on the DOT web site. I can recommend Terry Southam who contact details are on that list. Terry has done work for me in the past and I have found him very good. He may be able to recommend a welder to you as well.