Model 80 'Type 1' (386DX-16MHz), 27C256-120nS EPROM x4:

U52: FRU 72X7550 (internal FRU ID 72X7551)
U53: FRU 72X7553 (internal FRU ID 72X7554)
U54: FRU 72X7556 (internal FRU ID 72X7557)
U55: FRU 72X7559 (internal FRU ID 72X7560)
BIOS Revision '0', date of 30 MAR 1987

All below have the same relative internal FRU ID and BIOS date as above:

U52: FRU 90X8548
U53: FRU 90X8549
U54: FRU 90X8550
U55: FRU 90X8551