The original Generals system is totally disabled, wont work, but you can come close
The simplest ay to add the old Generals is to make each of the Generals into a SCIENCE, and make each of those Sciences required before you can purchase any other.
Lets say you play as USA. You already have say SCIENCE_USA as your 'intrinsic' science. Now, if you replace the first 3 Generals abilities with 3 Generals instead, say Air Force, Tank Command and Special Forces, you can then have it so that the next things need ONE of those Generals before you can use it.
Ive hacked up a quick JPEG based on something I did a while back to try and illustrate what I mean - see attached.
In the example there, its the USA. You can choose one of the 3 Generals, Air Force, Spec Forces or Tank Command. The Generals ablities underneath each one are only available to that specific General - you just give each one a PrerequisiteScience of the relevant General in Science.INI so you can only purchse that science when you have already chosen a specific General.
If you can get what Im on about here, youre probably half way there to doing it already
BTW, if you want the original Generals images, post here and Ill see what I can do. Unfortunately, none were ever produced for the GLA Warlord/Bio Command/Terrorist
EDIT: sorry, forgot the pic!