Back in 75 had my 68 FB 350 HO with 3.08's 140 mph. Still go'n but had to much lift. Manual steering felt like power steering.
Not exactly stock, but;
Next yr w/a 70 RAIII/th350/3.73's with taller tires.
Two yrs later w/a 70-455(same #12 hds and sft cam) with same 3.73's and tires.
Never got brave enough to try'n bury it.
FWIW, no spoilers.
Buddy had his 72 GP 400 with 2.93's spun back aroud to 10-15 mph few times.
Dont remember what top # it had had speedo. Think 120?