Here's a guess:

F3I0M
F 3 10 M
F = Flint, MI assembly plant
3 = March
10 = 10th
M = 3100, 3200, 3600, 3800, 4000 series with RPO-408 (???)

You'll need to find the block date casting code:
http://www.1954advance-design.com/Web%20images/casting-code-photos/codes-ser-nums.html

RPO-408 was a 265 V-8 option in some years