Beaware of used cylinders.

When buying cylinders and heads on eBay. I see miss dated cylinders. Look at the location of the studs. Some later cylinders have the studs against the sealing ring. The older cylinders have the studs away from the sealing ring.
Some are dated wrong. Make sure you match up your cylinder to the one pictured. Check and double check.

Are you specifically speaking of the stud difference between the 1979 and 1980 390 cylinders? I am not sure if the difference occurred in the lower displacement models as well. Since I have never owned a non primary kick 250 as of yet.

In the early years the studs were closer together with smaller transfer ports. Then they opened up the dimensions on the studs and increased the length of the transfer ports. In 82 they increased the transfer ports again size wise on the air cooled. This was kept the same into the liquid cooled engines. I'm not sure about in the late 70's as to what interchanges but you need to checkout the stud locations and the transfer ports. One of the Husqvarna parts sellers has pictures of the base gasket shown. I noticed the missed marked year wise cylinders on eBay.

http://www.husqvarna-parts.com/page/page/3736875.htm?page=2

Look closely at the base gaskets and the size of the transfer ports.