I know nothing about a lilac tree, but I would not move a dogwood until after it had dropped all of its leaves. There is an on going debate about fall vs late winter transplanting. I am in the late winter camp.

If you trim the canopy you may never have a natural looking tree again. Reducing some of the above ground growth could be a good idea but you have to be careful.

Your root ball ideas sound good to me...wider is better than deeper. Be careful how you lift the plant out of the hole. Very easy to strip/ damage bark.

Thanks for the advice,but if you move in later winter how do you water it? the ground is frozen and the water will pool and freeze?
Not going to use any power equipment on this... me and 2 strong teen agers. the area is at the back of my shade garden .
If I did do late winter moving I'd assume that I'd have to pre dig the whole before the ground freezes?
By "late winter" do you mean Late Feb? or March?

I am in MA we have What the Meteorologist say is winter Jan Feb March, we have Late Winter April some times.
We have Spring Late April May and Early June...Then we have Summer July and August,Then Fall Sept early Oct and early winter Late Oct Nov Dec..
So you can see my confusion eh? This is all kinda tounge in cheek...but ya get the drift. I am Zone 6 a/b ish..

My experience is limited to the deep south. We get snow once every six to ten years and it lasts only a few hours.

My thoughts on transplanting in late winter are based on considertion that a dormant plant's roots grow little to none over the winter and since cut/damaged roots can have problems, ... why not do the cutting right before they start to actively grow/heal?

Doing the transplanting in late winter also means you don't have to worry about any special care for the plant over the winter.

I suspect that in most cases, so long as the tree is dormant, it will make no difference.

I'd like to see some of the more knowledgable folks weigh in.

I'm not sure i would go through the work to try to move the lilac. I would just plant a new one in the sunny location. If there any limbs on shade trees you can remove to get the old lilac more sun, you can try that - if not, just cut it down and grow something that likes shade.

The dogwood, i would consider leaving as is. They are valuable trees. If you really do want to move it, a professional could move it with a tree spade. Its a mechanical piece of equipment that can carve out the root ball and put it in the new location safely. I would not do much pruning on the dogwood, just a little if its misshapen.