The 1st flowkooler I bought about 4 years ago did not have that huge gap, and it had way more vanes. With the gasket it was like 1/8" or less. This was in a mancini housing, 440.

I remember when I bought it I had to call them first because they had 2 part numbers on their website for BBM pumps, and I was confused on which one to order. Turns out they were changing part numbers. So, I think at the time I called they were phasing out the old design (probably from complaints related to the issues with the above posts) and that is why they had 2 part numbers. Now all the old are gone, and its just the new design that sits lower in the housing, with more vanes, possibly a different vane shape as well.