The tines you ordered require a another piece, that slips into the tine, and are held by a roll pin. This is the portion that you actually mount in the tine holder. Since the pin can be removed, and the tine changed, you can save a few bucks by not having to reorder the mount. FYI- I tried the R&R coring tines one time and had a tough time getting them to work. Seemed the side eject opening was smaller than the core itself. After a few greens of basically solid tining with hollow tines, I took them off and returned them to R&R. You can get tines from Toro or JRM. I get mine from a local aerification contractor. Not sure where he gets his.
As for the small cut out, the heads allow for multiple size tine mounts to be used. For instance, a 1/2" coring tine might have a 3/8" mount and use the larger portion of the hole. While a 3/16" solid tine will mount in the smaller portion. All with the same bolt.
When you first start the machine, run it at a slower RPM than you would think. I want to say were around 420 pto rpm at about .8mph.
Even though these books are from Toro, not much has changed. Maybe they'll be useful.
https://lookup3.toro.com/classes/doGetPub/?pubid=44325https://lookup3.toro.com/classes/doGetPub/?pubid=44338