window replacement in difficult situation

I have a circa 1950 house built from cement (or is that concrete?) blocks. The windows are all original and need to be replaced. I'm okay for most rooms in that I know how I will tackle them BUT I want to move my kitchen to what was formerly a bedroom. The windows there sit lower than the proposed countertop height. I don't want to spend the money bringing in a mason to make the openings shorter since this would get very expensive very fast!
Can I install the new windows to fit the existing openings and have the counters actually sit higher than the window sills? I thought I might build some wood boxes to fill the space so things didn't fall behind the counters. Windows would still be able to be raised and lowered.

Can anyone think of any reason this would not be practical? I tried to do a web search for an answer but guess I wasn't wording it right cause I found nothing.

Thanks!
MollyD