I wouldn't put it in my tank. No idea what it might leech out.
I made a skimmer stand by attaching a few pieces of PVC (as legs) to a piece of eggcrate.
I use to use one of these that I cut down to about 2 inches for my sump/skimmer combo. It worked well and because of the wide lip on top it would fit any skimmer base from 8 to 11 inches. Obviously you can cut it down to whatever rise you want for your setup.
Aftermarket Aladdin B-37 Basket Used as Replacement for 850001 Amazon product
As others have said, I also would not use the concrete block. I have made a variety of DIY skimmer stands out of egg crate and/or other aquarium safe plastics/acrylic.