1970 Mustang Transmissions can be identified by a metal tag attached to the case.
The 3 speed and 4 speed transmissions were available with 2 different sets of gears.
 
3 Speed Transmission Tags 4 Speed Transmissions Tags
RAN-AV RAT-BA RAT-BB RUG-AW RUG-AV  
      Close Ratio 4 speed Wide Ratio 4 speed  
1st - 2.99 1st - 2.99 1st - 2.42 1st - 2.32 1st - 2.78  
2nd - 1.75 2nd - 1.75 2nd - 1.61 2nd - 1.69 2nd - 1.93  
3rd - 1.00 3rd - 1.00 3rd - 1.00 3rd - 1.29 3rd - 1.36  
Rev - 3.17 Rev - 3.17 Rev - 2.33 4th - 1.00 4th - 1.00  
           
Used with 200 and 250 Used with 302 2V Used with 351 2V Used with 3.25 rear ratio Used with 3.50 rear ratio  
6 cyl engines.     gears and lower. gears and higher.
DATA PLATE CODE TYPE
   
1 3 Speed Manual
5 4 Speed Manual - Wide Ratio
6 4 Speed Manual - Close Ratio
V Semi-Automatic Stick shift
W C4 Automatic
U C6 Automatic
X FMX Automatic
Z C6 (SPECIAL) Automatic