Spectre G3 10/22 Chassis

[True Shadows]

Is there enough room on the picatinny rail of the st22 receiver for an lpvo in a cantilever Mount as well as an offset reddot mount?

I would say yes.

As long as you don't have a mount that cants forward too far so you can still get a good sight picture. (One that's straight up and down at the rear not forward would be best). If that doesn't work you could mount it at the forward end under the mount.