Finally started cutting into the plow.
First, needed to make a kickstand for the base unit, as it likes tipping over backwards (just square tubing at a 90º angle, slides into the mount I made to hold the engine for a powered bagger unit when I'm using it for mowing):
Here are pictures of the result for one side, held together with 9/16" solid steel rods.
I started cutting 6" lengths of thick wall 9/16" pipe, then drilled out the pipe with a 9/16" drill bit so the 9/16" steel rod would slide easily within it. Then I ground off the paint where I was going to weld the alignment pipe, lined up the pipe so it was parallel to the blade, then welded them in place. After this, I marked the cut line on the blade side, and used a cutoff wheel on an angle grinder to cut the end off, also having to flip it over to cut through the alignment pipes and some support braces on the back side.
This kind of worked, as I can get it together and it certainly feels very solid, but I need to use a BFH to get the pins in and everything together. Likely, the heat from welding the alignment pipes put some stress in the metal, and the curvature of the blade between the two sides is slightly off. Tomorrow, I'll try "adjusting" the curvature to try to eliminate/at least reduce the need for a BFH to get that side on.
When I do the other side, I'll try putting a "rib" out of 1/8" flat steel on each side of the cut line (on the back, like Warn did on the end of the plow) to minimize the warping of the blade (actually, I'm kinda torn about doing this, as it would make "adjusting" the blade more difficult if it does still warp). I'll also add these ribs to this side, just to strengthen the new end of the blade.
I also need to drill hole for another plow bolt to hold the scraper blade on the end piece in place.