The quickest <pun intended> way to find an E-Body option for a 1970 is to search HERE
Just hit CTRL+F to open the Find search box, type the option code, in this case S74, and hit ENTER or Return.
Answer: S74 Power Steering Quick Ratio 12:1
The window stickers showed S74 POWER STEERING-FAST RATIO
I have numerous broadcast sheets for A53 Trans Am package Cudas and Challengers showing manual steering (no numeral in the S77 box), power steering (7 in the S77 box), and Power Steering Quick Ratio 12:1 (4 in the S77 box).
FWIW - The standard steering was manual steering. The power steering and the power steering quick ratio were optional at $90.35. Quite a sum for 1970.
Here are two T/A window stickers. Curious enough, the Trans Am package cost $865.70 while a 426 HEMI engine cost just $778.75 in a Challenger. The A53 package was called out differently on AAR window stickers. The BS23 model became PLYMOUTH AAR CUDA-2 DOOR HARDTOP at $3,966.00 and the the A53 code showed no cost but was essentially $802.00 more than a comparable BS23 PLYMOUTH CUDA-2 DOOR HARDTOP at $3,164.00. The HemiCuda option added $871.45 to get the 426 HEMI engine.
No S77 or S74 which is standard manual steering for this Challenger T/A.
S74 code for POWER STEERING-FAST RATIO on a Challenger T/A.