Can you sli a 460 768mb with a 1gb

You can run them in sli as the bios string is the same so the driver wil enable while the only real requirement for sli is the gpu-s must be the same regardless of enabled shader count and memory path size. The penalties however will be that you will only have 768mb of usable vram but there will still be gains to be seen in sli. Memory does no double or stack compared to 3dfx and the rules are very much the same as crossfire for the exception of clocks.

In short it will work.
 

Legit Reviews disagrees with you.

We tried to SLI the original NVIDIA GeForce GTX 460 reference cards, but we quickly found out that you can not mix and match the 768MB and 1024MB versions of the GTX 460.
 

It is not a hardware limitation but driver, nvidia simply did not enable sli for these two cards. With the right bios editor and the right device id codes that can easily be solved.
 

That sounds like a bit more messing about than most people would want to get into. So I stand by my earlier post in that straight out of the box, it won't work.