any of these mobos fit my optiplex 780?
OptiPlex 780 Desktop
As you can see in the picture in the above link, there are four different sizes. You don't mention the one you have.
sorry, its a minitower
I would be careful with that swap. The 980 is kind of a unicorn. It's a BTX layout but not LGA775/771 which BTX came and went with. The 980 uses it's own cooling solution and I think the bolt pattern may be different. This is important on a Dell Optiplex because it bolts into the case directly, not to the MB or a backplate, or even removeable risers.. The classic BTX has the CPU turned 45* like the 780 does.
A built Opti 780 would have a Q9650,16GB DDR3 1066 RAM, and a Zotac GTX1050Ti Mini. A bigger GPU will require modding and a PSU upgrade.
If you need more than that I would suggest another computer. The Opti 780 was end of the line for Optiplex BTX layout.