I think you may be right about the VX9 stripes being a twister only deal. For comparison I'll show you what I've came up with on MyMopar decoder. Everything matches except A51 went from Sport Fury to Duster Twister in 1971.
VL29:
Plymouth Valiant,Duster
Low
2 Door Sports Hardtop
G1B: 318 230HP 1-2BBL 8 CYL
1971
Dodge Main, Hamtramck, MI, USA
354891: Sequence number
E44: 318 cid 2 barrel V8 230hp
D31: A904 3-Speed Auto Trans.
EV2: Hemi Orange Exterior Color
L1X9: Trim - Low, Unknown, Black
TX9: Black Int. Door Frames
407: Build Date: April 07
EV2: Hemi Orange Top Color
U: USA Specifications
A51: 70 only Sport Fury S-23
G36: OS Dual Racing Mirrors
J54: Sport Hood
M21: Roof drip rail moldings
R11: Radio Solid State AM (2 Watts)
V8X: Tranverse Stripes, Black
V9X: Longitudinal Stripes, Black
EN2: End of Sales Codes
