If the 1B boards are coupled together with the same connectors as the 1Fz then what you need are KEL 8811-100-170L-F, but unfortunately it seems like KEL no longer manufactures this connector, and nobody has any in stock. I was trying to do the same thing with a 1Fz board I had lying around and was unable to get the right angle plugs needed for the main board to allow it to connect horizontally with the right angle connectors on the secondary board.
Where I'm at right now is sourcing another brand of connector that has the same pin arrangement and 100-position contact that does make right angle plugs AND receptacles and I'm going to simply replace all 4 plugs on the 1Fz. (The big white connector in-between the two black connectors on the 1fz is purely for structural support, not a single pin is connected to anything and all 48 pins are connected to eachother, it can be ignored)
I just received some samples of a TE-Connectivity connector that looks promising, I will let you know if they work. It's possible there is another brand of connector that mates with the KEL connectors SNK used, but I have not found one, as most other brands use D shaped plugs for these kinds of connectors rather than the rectangular with keys that KEL uses. When I feel lke playing with the heatgun I'll swap for the TE connectors and test. Just need to make sure the pass-through order for the pins is the same on these as the KEL.
For reference, the TE connectors are part #1-1734099-0 (plug) and #1-1734037-0 (receptacle)
UPDATE: The TE connectors will not work because their pin arrangement isn't the same as the original connectors. Both the TE and KEL connectors have all 100 pins in 4 rows with the odd rows offset 1/2 pin from eachother. The TE connectors have the same rows offset for the plug and receptacle, the KEL have the even rows offset for the plug, and the odd rows offset for the receptacle. Additionally, the KEL pins have an odd pass through order. The TE connectors make sense, pin1 on row 4 connects to pin 1 on row 4 on the other side, the KEL have pin 1 row 4 on the plug connect to pin 1 row 3 on the receptacle.
Unfortunately none of these plugs I've been researching really show the order the pins connect, mostly because your designing a product around them, not trying to replace something else, it's really hard to know the pin arrangement and connection order ahead of time. I ordered samples of a ton of other brands of similar connectors, so we will see if any of the others work when they arrive.
UPDATE #2. One supplier got back to me and can order the proper KEL part, unfortunately I have to order $24 of them for ~$60, I really don't want to still not even knowing if it's going to work out. I received another sample from another company today that will also not work