First off, my Marlin sliders have been through hell & back over the last 6 years.  They are 1.75" .120 wall HREW round tubing.  They have 3/16" thick scab plates welded to the frame with small triangle gussets welded to the tops of the slider legs.  I've bent the sliders up to the point the doors don't like to open or close.  I need to build a new set that are beefier.  The frame is slightly wrinkled around the scab plate area.

I'm thinking of 1/4" 2"x2" square for the slider legs and the main body of the slider.  I was going to bend up some new round 1.75" tubing and weld to to the outside of the main body tube.  They will be angled up like the current slider.

Here's the current bent up slider




Question 1 - Are square tube slider legs stronger if they are rotated 45 degrees?  The diagram shows the slider legs in red. 

Question 2 - I know it's easier to weld the scab plates if they are rotated 45 degrees.  What about keeping them vertical and added a piece that wraps over the top of the frame?

Question 3 - How do I remove the current scab plates from the frame?  They are fulled welded on the perimeter of the scab plate.

Here's my cheezy frame and slider diagram 

Right on, thanks for the advice!  I'm thinking of making my scab plates 6-7" wide and running from the top to the bottom of the frame.  Currently, they don't run top to bottom and right above the scab plate is where the frame is wrinkled.

I might just reuse these sliders and add a forth leg to them.  Since the sliders didn't actually bend, it would save me some time.  I can just sawzall them off of the current scab plates, grind the old scabs off and reweld some bigger, thicker plates to the frame.  My slider arms are currently gusseted like this

V
O

With two small triangle gussets in a V pattern above the slider leg.  I might change that to one large one that extends further out on the leg.