Gas tank compatibility question

[Dan Halen]

I have just purchased a '78 750 and am not too keen on the gas tank styling.  I was wondering if anyone here knows if either the earlier 70's models or the 2nd gen. 79 and up tanks fit on my new bike?

[Re-run]

Any tank from 69-78 will fit. However, there are a couple issues. The 77/78 tanks are longer. So if you put on an earlier tank, you will have a bit of a gap between seat and tank.
You can replace the seat but the 77/78 hinges are on the left while the earlier seats were on the right. So you would have to reweld hinges or swap the foam and cover.