I did not get square dies. You will not be bending anything over 1" anyway. The larger tubes will be straight with miters cut to change angles. Any other bends are usually slight with a collective effect of curving a large radius.
The biggest radii will be with the 1" round tubing used up the windshield post. My windshield tubes have a bend around the lower corner of the windshield with a curve up the post and another radius over the top where that tube curves over the door opening.
The other location I used 1" tubing is over the wheel openings. Those tubes follow the arch of the fenders allowing a distance from the edge of the opening to provide a place to attach my inner fenders. These tubes also provide places to make fender and rocker panel mounting tabs.
A tip I recommend is to place masking tape straight down the tube and draw a straight line down the middle of the tape. Then when you are bending small "kinks" to produce a large curve, keep the line on the tape in the middle of the bender dies so the bends all stay inline. Otherwise the tube may have some strange twists that will be difficult to correct.
If you do want to use the round dies to bend square tubes, take a strip of flat steel the width of the square tube you want to bend and bend it to fit in the die, giving you a flat base to set the square tube. Then tack weld it in place (make them small tacks so you can break them or grind them off easily). That will hold the square tube in position when you bend.
RT