An FR691 is an FR691 is an FR691 regardless of what it is fitted into
The only difference the S number signifies is the trim , crankshaft PTO size & type of starter motor
The internals of all FR 691's are identical in fact the internals are identical across the entire 9 engines
So functional parts , rings , rods. rockers, pushrods, oil pump etc etc etc all the same
Some mower campanies require unique engine numbers to prevent owners getting parts from any where else but a franchised dealer and your engine would appear to be one of these
Your service manual is the one on the Kawakasi web page as it covers all variants of the 651/691/730 V engines .
If you read it you will see there is no refferance to much in the way of different parts
The specifications section of the service manual confirms that they are ALL IDENTICAL apart from the air filters , carbs , blower houses & starter motors + the presence or absence of an external oil filter
SO go to the Kawakasi web page / parts
Do not type in FR691V-BS32-R but rather click on the "Browse Engines - 4 stroke engine"
On the next page select FS691, note you have to hit the "show more" 4 times to get down the list to FR 691 link, then click on it .
That brings up the variants of the FS 651V engines.
Agin this is a looooooooong list so you might have to hit the "show more " tab a few times to go past all of the AS's then get to the BS's and finally down to BS section and low & behold, no 32 listed so it will be as mentioned before , Excel paid Kawakasi more for the engines on the grounds that the engine parts manual is not listed .