for anyone else, thats as confused and clueless as i was.
my advice is go to : https://toyota.epc-data.com/ and enter your 17 digit chassis number, from your cars registration log book, into the search box, in top corner of site.
it'll bypass all the thinking and confusion, and put you straight to your cars parts.
you have to click on the 5 digit number, in the schematic picture, of the part you need, to open up a 2nd box, with the actual 10 digit part number.
the 2 gaskets i was looking for, come up as :
22215-74380
22271-88461
and ive been looking for an exhaust hanger bracket for weeks too, which is :
17508-74080
its easy when you know how, confusing when you dont