Yes. It works just fine in mine. Understand that the G3 kit is a little different, and much less expensive, than the HK 91 kit.
After you install the kit, when you go to charge your weapon, do be careful to only pull the charging handle back just enough to clear the case head of the diminutive 22 cartridge.
The G3 kit is designed for use in rifles with the safety sear or auto sear arrangement. When the sear engages the hammer, the toe of the hammer is kept "flush" and allows easy reciprocation of the 22 long rifle bolt and carrier assembly. Because there is no autosear on your PTR91, the toe of the hammer protrudes into the path of the 22 long rifle bolt carrier, and can cause the subcaliber kit bolt and carrier to get hung up on the toe of the hammer.
Easily enough to clear this sort of jam, but why?
Some guys put a 2" length of hose over their mainspring before reinstalling the buttstock to prevent the sort of jam I just detailed. Myself? I just stay really careful to only pull the bolt/carrier assembly back far enough to chamber a round. I have no issues at all with jams.
The kit is a great addition to a great rifle. Makes plinking a whole lot of fun.