Wow! as always this forum have Seiko gurus providing valuable information. Thank you BodoWell.. You have three types of crystal. Possibly four. Mario is spot on with the part number I should say.
It depends on what profile you are after. It then depends on the year of the watch.
For instance anything post 1972 would more than likely have had a type 2 crystal. After that from about 74 or 5 it was a type 3. Anything 6105 from 68 to 72 would have had a type 1 until Seiko had loads getting replaced due them being chipped etc. Which is why the type 2 was made.
There are many superb threads out there and a blog by MartinCRC about them.