The hottest car I have ever ridden in was probably something like your first GTO except it was an SS 396 Chevelle.
I used to kid this guy who had a VW because my 55 Ford would eat his VW alive. Some time around 1967 or 68 he got the Chevelle. I have no idea what he did to it but it must have been running 500-600 HP.
He took me for a drive and going around 30, he floored it. It threw me back into the seat like I have never experienced. Much hotter than the stock GTO.
My first GTO was never bored and stroked, but the heads were extensively reworked, an Iskendarian cam and anti-pump up lifters were installed, the 4-barrel Carter carb and the stock ignition were tweaked, and a pair of Doug’s headers were installed.
I had a close ratio 4-speed with a Hurst Quick Shifter and a Hayes lightened flywheel and clutch. The 12.25 time slip was a result of a FRiend loaning me a 4.11 Posi-traction rear end and some 8” slicks. Street gears slowed me down by about a second.
The only suspension mods were Air-Lift airbags in the rear coil springs. Rest was stock stuff. The car hooked up really well!
It looked like a street legal “A” stocker, but it was not, strictly speaking, stock. OTOH, none of the competition in South Texas (Corpus Christi) was either!
As an aside, if you remember the old days, I saw Don Gay’s ‘66 GTO Funny Car “Infinity” race a number of times. I’d like to say I was able to meet him, but I never did.
PS My first ‘65 was a babe magnet!
My current wife will not let me use my second ‘65 to attract babes!
LOL!