When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Corvette Frames http://www.71corvette.com/frames.html
The body mounts were changed to rubber in 73 which some use on earlier models to help w/ the creaks.
A 82 frame can be modified to work in a 69, but I'm not sure it's worth it.
The rear section of the frame is different, to accommodate the the impact absorbing bumpers. The trans cross member on the 82, doesn't have holes for dual exhaust pipes to go through, and the 80-82 rear end incorporates the mounting cross member. The 69 rear mounts to a crossmember, that's part of the frame. There are also some miner differences to the front frame horns, and the mounting of the gas tank.
The number of body mounts, and their location, is the same on all 68-82 frames. The 73-82 frames did use rubber body mount cushions, instead of the aluminum mounts used on 68-72, but this doesn't effect mounting the body. GM went to rubber mounts, as part of the modifications made when they went to radial tires, in 73. Many Corvette owners have used the 73-82 rubber mounts on earlier Corvettes, to improve the comfort level of the car.
The basic design of the C2 and C3 chassis were the same. There were some modifications through the years to accommodate feature changes that were 'required' (ie, improved bumper construction, Endura bumpers, additional safety struts, etc.). There is no similarity of this "ladder" type design to the chassis of the C1's or to C4's and later Corvette designs.
I think your best candidates for a '69 car would be frames from '68-72. A '73 frame would be the next best choice. '74-79 frames would be easier than the '80-82 units.