A904 vs A999

Maybe some one can shed some light on what make's an A999 heavier duty I've had very little luck finding info everyone keeps saying "Dodge? oh you meen a 904 tflite."
1st How do you tell the difference between the two ?
2nd Do A999 have a specific casting #?
3rd Are 1st, 2nd, and drive gear ratios the same? ( I've always thought the A999 to have a stiffer 1st gear but no meens to confirm it, my 74 dodge service manual doesn't tell me anything here.)
4th lastly the fender tag code just refers to having a Tflite were do you find out which one or is that just an engine pairing thing?
(E-58 LS29L4B If this helps any)

Any info or insights will be appreciated,Thanks!!!!:read2::read2: