How to modify for less? Learn for 'Do it yourself', buy stuff on-line like Summit Racing. Where to start? Upgrade the brakes. Change to front disc if it's already. Upgrade the ignition. Get rid off the points and change to modern electronic then increase to spark plug gaps a little. Change the intake system for better breathing.
1968 In a fastback is nice, although as a coupe its less desired than a 1964 1/2 through 1966, the coupe has sunk in tail lights, the high beam headlight switch is on the floor board for the left foot to click, it comes in a inline 6 cylinder or 289, as a 289 it can come in a GT or just 289 you can tell the diffrence between the 2 simply by looking to see if its exhast comes through the rocker pannel that would be a gt, it could have a c3 transmission, manual, or a c4 tranmission, automatic, the number means the amount of gears it has.