Ok so far, with a 64 GTO I was able to sqeek out a 9.05. 
Now thats with Race suspension. (changed the spring rate, sway bar, camber, sway bars and ride hight, all stuff I did to my real gto.)
369 HP, (racing exaust, balane, chip and valve job)
the full custom tranny. Set to 
 
First Gear Ratio: 3.28:1 
Second Gear Ratio: 2.13:1 
Third Gear Ratio: 1.57:1 
Fourth Gear Ratio: 1.24:1 
Fifth Gear Ratio: 1.00:1 
Sixth Gear Ratio: 0.76:1 
Rear set to 3.55
This is the exact gear setup my GTO had. 
2 way posi. 
Sport tires soft.  Now I did the tires cause I think when you chose road it sticks you with REALLY crappy tires prolly based on the bias ply redlines it came with in the 60s. 
I could get a better time, I spun it three times atleast. lol.  No driving aids at all. 
I tried witht he regular tires and the car would not stay strait even on a straitaway lol.
Oh thats from a rolling start on practice from Sim mode? Do you start from a stop in arcade?
Was fun, and on the long last strait it topped at 155 I think, not tacked out but out of power.