lock-up stuff
Ok, I gave you the readers digest version for an answer. Let me get more specific.
When you drop the pan, you will see the valve body held to the case with approx, 17-19 bolts. The switch I mentioned can be obtained from a transmission shop. Seems they are becomming rare. The owner of the shop let me look through his valve bodies and I found the one I wanted. They probably can be ordered.
Now lets explore two options:
1. If you want your corvette to remain mostly stock, then use the method I mentioned earlier. What I forgot to mention is that the speedo has a sensor that at about 23 mph, juice is sent to the switch (2nd gear switch) and lock-up is available, the computer furnishes the ground. What I did was to take the 2nd gear pressure switch out of the mix. The speedo sensor still sends power to the new pressure switch, but the switch is grounded to the case and when approx. 38 is reached, lock-up occurs. The computer no longer furnishes ground. If the computer goes south, lock-up will still occur.
In my opinion lock-up at 25 mph lugs the motor to much. Now lock-up occurs at about 38 mph, much better for the engine.
Option 2: I have built several streetrods and this is how I handled lock-up on a 700-r4. This is a 350 with overdrive. I have run power to the solonoid pressure switch thought a dash mounted switch and grounded the pressure switch to the case. When I turned the dash switch, lock-up would occur. I put a safety switch on the brake pedal and when putting on the brakes, power was cut to the trans, lock-up was turned off. Remember, lock-up would only occur once 38 mph was obtained, thus when the speed dropped below 38 lock-up turned off. On the next project, I eliminated the dash switch and ran fused power to the lock-up solonoid switch and used a vacuum switch that would turn off lock-up upon ecceleration.
In the streedrod world, the lock-up is handled in this manner. By the way, several lock-up kits are available from

suppliers such as Jeggs, Summit and many others. The kit contains all the parts needed to hook up the pressure switch as mentioned. The kit is about 100 bucks but well worth it. It comes with great instructions too.
I hope this helps...
Bill