Help decode serial number

[RBaker]

The 38 Ford truck serial number on my frame has a letter "I" as the last digit.

It looks exactly like this on the frame *18-464258I*

Would my serial number be 464258?

or

Would it be as the Vanpelt website list serial numbers such as 18-4, 64258I?

The "I" being a number 1 even though it is a definite letter "I"?

I was not reading the number correctly the last couple of months due to rust/dirt etc...