Grade 3 will be grade 3 no matter what you do. The paper's contrast curve is what it is and changing the light source will not affect that. Going to a diffusion type light source will help a little, but only just. In reality, all that really changes is that the transitions from dark to light tones become a little smoother.
Pre-flashing the paper will help a little, and it works by raising the fog level. If you're not careful, you wind up with less than clean whites and/or muddy shadows. It works with some images, but it's not a panacea.
Pulling the paper before development is complete is almost asking for trouble. Paper develops fast, and it's too easy to get an unevenly developed print that way. A soft working developer is probably your best bet. If you can source Selectol Soft or something equivalent, try it. There are lots of formulas you can mix up yourself that will give similar results. But before you go through all that trouble, you could just try diluting Dekol 1+4 or even 1+5. It won't have much capacity or tray life, but it will act like a soft working developer. If you look at the soft working developer formulas, you'll see that they contain less alkali, less developing agent (usually metol), and more bromines than standard developers. Adding a measure of well used and partially exhausted paper developer to a more dilute working solution of Dektol will accomplish that.
In the end though, the best use of the paper would be to use it when a hard paper is called for. That's how it was designed and that's how it will work best.