A lot of sellers post "stock photos" and not photos of actual piston.  My memory is not perfect but I'm pretty sure the Wiseco I bought for a 100 had the windows? 

I just looked on ebay and yes, there are pistons there with the box that definitely have the cutaway and not the windows.

Trying to remember but I vaguely remember now that what I used was an RT100 Wiseco Piston along with some other RT100 parts because the DT100 parts were NLA and RT100 parts would work.  I think the RT100 Wiseco might have been like $20 cheaper at the time?  

Tinkicker we both have the same pic, mine via link up in #3 i think, but the ebay site said 52mm on mine which of of course is std size.
If your link had 53mm=1mm over & same number on top then hell i dunno haha.
What Mark says makes sense although i googled wiseco 11221 & came up with nothing useful.
Wiseco numbers i've seen are nothing like that normaly.
photos.app.goo.gl/DgFtjh5NYFEmGcht5
Ebay UK by the looks. 1mm over=53mm with holes.
Just thought might help if in the end you decide to buy again if yours is 'too not right' to be used but lets hope that's not the case.
eBay item number:350470027872
New For Yamaha RT100 DT100 Piston Kit + Rings 53.00mm DT RT 100 +1.00mm

Ok wow so I looked again and sure enough there is a cutout on the intake skirt! Im so used to seeing the windows on my other Yamaha stuff or deep insets like on my modern Husky(ktm), the cutout didn’t register. So I’m not sure of the cutout instead of windows makes a difference but I’ll run it.
Thanks for the help guys, sorry I’m a bonehead. If anyone’s interested I’ll start another restoration thread and post pics if the pic embedding is working. It’s coming along well. Still need to find a decent clutch and mag rotor. 

Great stuff, we have a winner & you don't have to buy another kit.
She'll go good & likely run better than ever.
Go fast bikes had the cut away--well--not all but most.