I had gotten a sears snow plow/dozer blade but it didn't have the piece that slides into the mule drive slot. Thanks to Alan for taking lots of pictures, with a tape measure in one hand, and Ryan for drawing a sketch, I finally had a mule drive cut and the bracket that is circled in picture 2 here, welded on . For reference, you could check here:
I needed another one of those arms that attach to the top of the axle so went ahead and got one the same size as the lower arms. (See the lower arms in my first picture)
My question is this: Is the axle actually what pushes this thing? I thought the mule drive piece would be tight in the slot but it is actually forward about 3/4" to 1 ". It seems like if it were tight in the slot, that would put pressure on the frame also. I did read somewhere that that top arm isn't needed at all but not sure what to think. I haven't removed it yet to see if the plow would be sliding back and forth.