I think "PBA" is just a prefix to an intel part code. But it seems to be consistent with anything made by Intel.
I only have 1 LPX board that uses the type of riser you're showing here, but it's an AST made board. There's another Intel made LPX board that I'll be getting soon which is without the riser card, so I have the same question about interchangeability.
If you have a look at the manual for that pentium board in section 1.10.11, it lists the full pinout for the riser card as J6E2: https://www.fermimn.edu.it/inform/materiali/e … bd/28181002.pdf
You can find some riser cards on ebay if you look for "eisa riser", since the connector is an EISA slot. Electrically, the way Intel made these is by matching up the ISA pins of the EISA slot with the ISA pins, with the PCI pins being deeper down and seemingly matching up in-order as well.
I've just confirmed that the ISA pins match up by plugging a basic ISA riser into my AST LPX board and the power pins all match up with where they should be for an ISA card to use.
What are the chances LPX risers would be interchangeable?
For the ISA pins, it's unlikely someone would want to re-design the wheel and they'd just map the EISA-ISA pins to the regular ISA pinout.
For the PCI part, well that could be different, as the EISA 32-bit bus isn't the same as PCI, so they would have to decide where pins go. But on Intel made boards, I think they'd all be the same as that pinout in the manual I linked.
Potentially, I can pull the riser out of my AST 486 and see if it matches the intel pinout for the PCI pins.