"1" would be a 3.00 and "I" would indeed be a 4.11. It's doubtful that FoMoCo would have factory installed a 4.11 in a 390 as they were not very high winding engines.
But,...........I have seen stranger inconsistancies than that. 
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Alex Denysenko
Co-Administrator and Moderator
NHRA/IHRA/SRA member and licensed Superstock driver
MCA member# 53321
NHRA and IHRA SS/LA National Record Holder '00, '01, & '02
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
Professional Manwhore
The Barry of BarrysGrrl
Quote #1: "I never met a magazine mechanic I liked."
Quote #2: "Make sure brain is in gear before engaging mouth!"
Quote #3: "If you can't run with the big dogs, stay on the porch!"