suggestions on home made step notch

[blazer2007]

I,m wanting to do a small step notch on my 78 blazer but would like some ideas on thickness and size of metal 2x4,2x3 etc.I would like to make it bolt in good enough to get it to a welder.I can take the peices down to the welder to do the sides and such. as I have only a 110 wirefeed.P.B. wants $200 for one and then with shipping etc to Can. would be in the $300 range.All I want is level with the frame or a inch above.I already have a c notch but I need more, always need more.Here is a pic[not mine] of where I was thinking of putting the top bar