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IBM PS/1 PRO Model 2123 and PS/2 Model 25SX planars

Probably. The PS/2 Model 25 and 30 series always shared parts, including the motherboard, and the PS/1 "Pro" 2123 is really what would've been the PS/2 Model 30-386 or 30SX until IBM decided to rename it as a PS/1.
 
Nope they are not. The PS/1 and Valuepoint are different from eachother and different from the PS/2 and AT especially WRT:
  • Fixed Disk Parameter Table (the 1991-1993 386 systems from IBM needed a specially modified kernel in order to use the IDE controller or to boot using UNIXBOOT.COM)
  • Programmable Option Select
  • Disk Caching
Are you sure that the Ebay photo is a 2123 PS/1 and not a PS/2? A lot of the boards from that era look very similar. They all share a NLX board layout and a slot riser of 3 or 5 slots in the middle. I can send you very detailed photos of the 386sx PS/1 boards for Fall 92 and Spring 93 systems.
The PS/1 2133/2155 systems with a 386sx CPUs look like the one in this Vogons thread. There is also a similar (but not identical) board on the ValuePoint 325T/S (also listed over there).

PS/1
For the PS/1 systems there was only one 386sx board (with varying VRAM and RAM). It contained:
  • CPU: Intel 80386sx
  • Optional FPU: Intel 80387sx
  • Chipset: Chips & Technologies 386/AT 82C305 (VL82C305-FC) Uses 82C305 Data Buffer
  • Keyboard Controller: 8042AH Universal Peripheral Interface 8-bit Slave Microcontroller
  • Floppy Controller: Intel 82077AA
  • CMOS: OTI M10S0570
  • VGA: Cirrus Logic CL-GD5410 with either 256 or 512KB of RAM
  • RAM: OnBoard - 2MB or 4MB and two 72pin SIMMs


ValuePoint 325T
For the ValuePoint system there were a few slight differences:
  • CPU: IBM 386SLC Processor (a completely different beast)
  • FPU: Cyrix 387SL FPU
  • VGA: Cirrus Logic CL-GD5420 with 512KB or 1MB of RAM (twice the RAM)
 
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