F55Y indicates 1955 car 235 installed with RPO313 Powerglide transmission. That engine would have come from the factory with hydraulic lifters.
3701187 & H123
Wait to hear from someone else, but could that block casting code be 3701887 (1953 235 truck), and H123 be August 12th 1953?
You posted that you have a GMC 3100. 3100 is a USA Chevrolet truck 1/2 ton designation. USA GMCs did not use the 3100 designation.
What year is your 235? Is it a 1956 truck 235 (mechanical lifters)?
