I have purchased some gaskets from one of the suppliers.  They fit but they are smaller in diameter, restricting flow.  Instead being 35.5mm it is 31.8mm.  Considerable difference and if I add up the four outlets' together, it would be almost 16mm of flow restriction.  
It seems to be an American size, 1 1/4 inch which gives me the hint that it is for an American car originally.  The vendor might not even know it or hopes it won't be detected.  Similar but not the same.  
The question is; does the flow restriction result in worse performance?  Can I install it without loosing power?
Or should I send it back to the vendor?  They might say I did not buy it from them.
Zoltan