The problem appears to be your piston. The wrist pin is too high up. All of my China Girl pistons have the wrist pin closer to the botton of the skirt. Yours looks to be more toward the middle of the piston.
Between these two cranks there's no difference between the stroke, or the rod length. There are several other differences though.
For the sake of discription we'll refer to the crank with the fly weights that bolt on to the fly wheel as old style, and the crank with one piece fly wheels like yours, new style.
The main differences I measured are,
The overall width,
Old style crank, 105 mm. New style 101 mm
Crank pin width,
Old style 11 mm, New style 10 mm.
crank pin diameters are the same
On the power side of the crank, the shaft legnth is the same on both cranks, 42.5 mm. On the magnito side the shaft on the old style is 1 mm longer. 32 mm vs 31 mm for the new style.
Overall weight. This will vary slightly because the bolt on style fly weights vary in weight somewhat. I've seen as much as about 10 g difference on the bolt on fly weights I have. I'm not sure about the new style cranks because I've only looked at one.
Total weight,
Old style 1574 g, New style 1392 g
Overall fly wheel diameter,
Old style 90 mm. New style 89 mm.
