an fe block won't have any numbers that will tell you 100% what it is, as you could swap out the cranks and have a 427, 410, 390, 360 or even a 352 (unlikely). the only way i know of to see without pulling the motor and removing the oilpan, is to pull the intake and a head, and measure the bore and stroke.
Woodz can tell you a whole lot more than i can, but here are some dimensions...
... ... bore x stroke
390ci 4.05" x 3.78"
406ci 4.13" x 3.78"
410ci 4.05" x 3.98"
427ci 4.23" x 3.78"
428ci 4.13" x 3.98"
if it was me, i'd wait for Woodz reply before i started pulling the intake
you might check out club cobra
they have a pretty good fe forum...
and if i'm not mistaken, the date codes on fe blocks are right underneath the oil filter adapter, upside down of course....