OK, I'm going to do a quick step by step of putting Dawn clothing on Diva using the PRO version of Poser (9+). Since you need Copy Morphs From, you will need the PRO version to make this work.
Load Dawn normally
Load your choice of clothing and conform it to Dawn.
At this point, ensure the following options are checked on the Properties tab of each clothing item.
Once that is done, select Dawn>Body on the figure dropdown menu
Inject the Diva morph in Dawn.
Select a clothing item from the dropdown menu - Shirt>Body for example
Then, Figure>Copy Morphs From and choose Dawn from the popup menu
You will be presented with a window listing all Dawn's installed morphs. Uncheck Dawn/Body, since we only need to transfer one morph.
Scroll down the list until you find plDiva and click in the box next to it, then OK
At this point, the clothing should automatically fit to Diva, though there may be some crushing we need to fix in the next step
To smooth out crushing from the scaling
With the clothing selected (Shirt>Body) click on the morph brush tool
When the morph tool menu appears, we will go through a series of steps to alter the Diva morph and rid the clothing of the crushing.
It doesn't matter which body part you select, but I try to start where the crushing is the heaviest. You are not limited to this body part, so it really doesn't matter where you start.
Drill down in the menu for the Diva morph
As an aside, I always turn down the magnitude when working with the morph brush. The default setting of 0.5000 is simply too strong, even for intense crushing. Brush size depends on how much you want to cover in one stroke with the brush.
Choose the Smooth brush from the icon in the morph window and start to paint the smoothing morph over the crushing. You can smooth all the crushing in one go, regardless of body part. No need to go through the morph selection process for each one.
Once you have finished editing the morph, you can Zero out the Diva morph in Dawn and save the clothing item back to the library. By doing so, you have permanently altered the Diva morph in your clothing and the next time you use Diva, the clothing will autofit and auto follow Diva.
Here, I used this method to put the Pixieluna Must Have Casual clothing on Diva.