Someone asked this question on another forum, thought I would post it here for the knowledgeable ones to answer
"Anyone know why the T-660 is a five digit unit number and the T-700's are just four digit unit numbers?"
Also, lots of nice photos here of Millis trucks if anyone is interested.
http://hankstruckforum.com/htforum/index.php?topic=47096.60;topicseen
Ron