rf855657.exe 8556/8557 reference diskette v2.10 -supports SLC2/SLC3 upgrades
8556/57 Diags Disk Ver 2.04 or better supports all 8556/57 386SX / SLC systems, including 8556/57 systems with processor options: 386SLC, 486SLC2, and 486SLC3.
8556/57 Cached Processor Upgrade FRU 92F0078
Note the unpopulated jumper "BYPASS JUMPER".
Not having one in-hand, I see the wires from the OS1 outline, going under the heatsink.