FY1 was NOT available for the full 1971 model year - it was a late addition - so its apparent lower numbers aren't a fair comparison to address its popularity
are you sure the subject HEMI Challenger R/T is FY1 "lemon twist"? it is 3-weeks earlier than the first FY1 e-body I have data on when was FY1 re-introduced?

the CANADS spec. 1971 HEMI Challenger R/Ts:
JS23R1B211139 to Crane Valley, Saskatchewan - HEMI automatic, "lemon twist" (I have this car in my notes as "citron yella") * NO DANA w/SHAKER

JS23R1B144517 to Montreal, Quebec - HEMI 4-speed w/3.54s, FC7 - "plum-crazy w/white" interior * NO SHAKER
JS23R1B242274 to Laval, Quebec - HEMI 4-speed w/4.10s, FJ6 - "green-go w/black" interior * SHAKER

JS23R1B251607 to Belleville, Ontario - HEMI "light green metallic w/black" interior (per the FAKE fender tag) * originally GF7 auto NO DANA & NO SHAKER
JS23R1B??????? to Rexdale, Ontario - HEMI 4-speed, FC7 - "plum-crazy w/white" interior * SHAKER

anyone have corrections/additions to the above list? anyone have the fifth VIN for the other HEMI R/T?

top 5 colors for '71 Challenger R/T (JS): FC7, EV2, GB5, FJ6, GY3
top 5 colors for '71 Challenger (JH): FC7, GB5, GF7, EV2, FE5