If you take this info:
A number of crate motors made by GM in Mexico, may have an "M" or "ML" prefix stamped into the front pad of the block followed by a series of numbers which is the serial number ofthat particular crate replacement motor. You may also see a raised casting on the block or heads of "Hecho en Mexico" which means "Made in Mexico". Many of the new GM crate motors are being made in Mexico. Later model crate engines, sold over the counter by Chevrolet or GM Performance Parts, may have different prefix code identifiers stamped in to the front pad on the block, such as "ZZ3" or three letter codes such as "XXA".
http://www.chevy-camaro.com/faq/chev...-decoding.shtm
and combine it with this info:
VF292800 – is an example of a over the counter crate engine. “2800” is the last 4 digits of the GM part # for the crate engine assembly. The final digit could be a year code. Another example: A Targetmaster engine (p/n 14009800) built in 1985 could have a code stamped as follows: A0198005 (A = january, 01, 9800 = pn, 5 = 1985)
http://www.nastyz28.com/chevy-engine-code-stampings.php
With the MM being in first and the 800 being in the at the end it may have been a transitional period at the mexico plant for the crate engines.
Just throwing ideas out there.