What the difference with frames between 68 to77?Besides auto and 4 speed,are the body mounts different.The reason I'm asking I have seen them here and on e-bay for about the price I was quoted to fix mine. Just another option for me to look at.

There are minor differences in all of the year models. Some are harder to overcome than others, tho. The biggest hurdle is the bumper mount systems, which changes the frame ends considerably. The rubber bumper frames from '75 up are prolly the most consistent, but there are still some minor changes in those too.
If you happen across a frame for a '75-'77, that would be the best, as far as easy swap-out. Other year models will most likely require some modifications, but not too much.
Larry @ Corvette Specialties(or other members) can prolly give ya more specific info on year-year changes.

Joel is right.  The two main differences are the transmission mount between manual and auto, and the rear bumper mount.  You can use an auto trans frame for a manual, but not the other way.  If you can save the back 18" of your old frame, you can cut off the new one and graft yours on to solve the bumper mount problem.  That only leaves little things, most of which can be solved by saving a tab or bracket from the old frame, or by using the equivalent from the new frame.  An example of this is the bracket for the clutch cross shaft. 

We sell decent used frames for $700 to $1,000, to give you a comparison.  I am sure you can find something closer to home in that price range.  If you do replace your frame, be sure to replace the front to rear brake and fuel lines, as you cannot replace them with the body on the car.

Larry