Thank you very much for doing those excellent drawings - they clarify graphically what I was trying to convey. One picture/thousand words and all that. I tried doing a free hand drawing based on some dubious assumptions, but I could tell real quick it wasn't going to work. Nice catch on that slight dogleg in the longer arm. I didn't see that.
The geometry and tracking of that arm are impressive. I'd love to have one to check out thoroughly. There's a similar American arm called a Van Epps. I've seen one, but never had the chance to use it. There are pictures of it in that "angling for 90 degrees" thread. It's very lightly built, especially in comparison to the B-J.
The weight of that arm, which I envy you for having, is going to be important when it comes to choosing cartridges. For the last two weeks, I've been using a Shure SC35C conical "DJ" cartridge and I strongly recommend it. The VTF with the stock stylus is 4-5 gr., but if that makes you uncomfortable, the N35X stylus works in the SC35C body and tracks at 1.5-3 gr. I've used the SC35C in a heavy vintage Rek-O-Kut S-120 - with the stock stylus - and in a very light DIY linear tracking arm using the N35X stylus. Your arm fits somewhere in between those two arms and I'd be very surprised if that cartridge didn't work well on your arm.