I ordered my '64 Custom/427-T with the mandatory 'HD' suspension and brakes and a 4.11 rear end. It was delivered to me in February and within several weeks I had installed Traction Master anti-spring-wrap bars, created and installed a deep oil pan to limit oil-pressure woes, and put spring jacks in the front coils and a re-calibrated front alignment. Eight inch M&H Racemasters took up residence in the trunk and for daily use a set of tall Atlas Bucrons went on the back to go with the 6.70-15s that came on the front from the factory. In March, we decided to go to Florida to spectate at the Twelve Hours Of Sebring. I swapped the 4.11 for a 3.50 and disconnected the speedo cable to preserve what was left of the 90 day warranty that was specific to the 427 engine. I'd installed a Sun 'Super' tach so we matched engine speeds in 4th gear with a friend's speedometer and I made up a small chart on a 3X5 card and taped it to the dash.
3000 on the tach equated to about 70 MPH. Except when I planned a weekend at Milan or Detroit Dragway, I left the unlocked 3.50 in the rear. I replaced the speedo gear with one that matched the gear and tire size.
The spring jacks in the front coils raised the front of the car by a couple of inches. Conventional wisdom said that raising the front of the car helped weight transfer to the rear and assisted the launch. It helped create the highly desired 'Gasser Look' and the only drawback was at high speeds. Starting at about 130 the front end feel would get light and float-y.
I'd busted off the output shaft in the T-10 trans and ended up walking home one night. I knew the Executive Engineer at T&C Livonia, where I worked at the time, and he released to me a then-not-yet-in-regular-production big in-'n'-out Toploader to replace it. I put it in, along with a Hurst shifter, and including the necessary new clutch disc, throwout bearing and output yoke. (I had to get the last three pieces from a dealer who specialized in big F-Series truck parts.)
I discovered that, when I came upon some sort of chibrolet 'performance' car on the highway, and a challenge ensued, it was possible to shift back into 3rd gear at a speedo-indicated 100 MPH. It not only made for an excellent 'passing gear', it often discouraged the 409 or corvette.
If we actually got it on, I could not only watch the tach, the speedometer was marked to 120, and the needle would go past the markings. Just to the right of the speedo was a red 'idiot' light marked 'GEN'---although the engine came equipped with an alternator. The speedo needle passed between the indicator bulb and the lens and was visible behind the red lens at about 130. If I shifted back into 4th when the needle disappeared, I was doing about right.
Coming back to Detroit from East Lansing one very early morning after taking the girlfriend back to school after a weekend home, I got into it with a corvette. I was probably going about 70-75 and he came up on me at about 80. I pushed it up a bit, and he did the same. Previous experience required me to look over at him with a big grin as I, quite ostentatiously, downshifted to 3rd at 100 and then nailed it. Soon after going back into 4th, I began to notice the float-y-ness but I was only half-a-dozen cars ahead and he hadn't quit.
Luckily we were on a long straight area of I-96, because I didn't let off until I was past 6000 on the tach. The car was so float-y and light that I was steering with only thumb and finger of each hand so as to not put in too much input. With the already-established extra altitude on the front of the car, the air-flow under the car was almost enough to have me doing a wheely. It settled down when I let off.
The corvette was simply a pair of lights in the far-back distance. God is sometimes extra kind to fools.
KS