This is going to be a two part answer and question
First. There are no unit numbers listed in the encyclopedia anywhere. You can see unit numbers when purchasing
*IF* you have "Show ID Numbers" = YES found in the Game Options screen under the MISC tab. If that is set to yes you will see formation numbers to the left of the formations of the purchase menu and to the left of the units after you select a formation you want. As I recal that is set to NO as default. For obvious reason I have it on all the time. "Normal" players rarely need to know that info.
The very, very best way to get the info I need to eliminate the guesswork about which unit people my be refering to is by using MOBHack. I assume ( yes... we all know what ASSUME stands for.....) that anyone working with OOB issues would be using MOBHack not the game as there are all kinds of ways to find and change things quickly built into MOBHack. So that brings me to the second part of this post
You say at the very start.....
OK....... in the USA OOB in the game there are 5 M1A1's still in service in 2010. Two are MCBS and I'm not concerned with those. That leaves three and all are already upgrades above a "standard" M1A1
#484 = M1A1HA+ Abrams ( a standard MBT )
#636 = M1A1 AIM ( National Guard formations )
#650 = M1A1HA+ Abrams ( CS )
#484 is already up to M1A2 standards so I don't know what mods I should make to "Mods needed per refs above existing M1A1 ABRAM levels " unless the M1A1's have been upgrade to M1A2 SEP levels and if that's the case the M1A2 SEP is right there in the game.
Don