[Henry Schmidt]

I'll come at the question from a slightly different perspective.
I don't know who made these rods. In 40+ years of building these engines, I have never seen that design used in an air-cooled Porsche.
That said, does it really matter? If you were thinking about buying these rods, "who made them" becomes far more important. You own them, they look to me to be well made and you have a history of success with them.
If this is a 2.8, that would suggest that the B&S is 70.4 x 92. Very common in the day. Whoever built this engine was looking to improve the rod length to stroke ration in an attempt to help it rev. 141:70.4 = 2:1. This odd length may also suggest that the rods were designed for another application. Carefully measure the journal size.
2:1 is considered by many (including myself) the optimum ratio for NA engines for a couple of reasons. Increased rod angularity causes additional wear and often facilitates the need for off-set wrist pins. Longer rods reduce angularity and create additional piston dwell improving horse power output. With longer rods, the pistons dwells longer at TDC and it dwells less at BDC. The decreased dwell BDC can cause detonation. The perpetuity towards detonation in a Hemmy head engine means attention to dynamic compression becomes more critical.
Knowing who made them is a nice foot note but not required to rebuild your engine.
Obviously the long rod will create the need for custom pistons, so look to that issue carefully.