T cases and X cylinders is the standard 96+ Superjet engine.
The T cases are for dual carbs and have better intake passages and angles than older cases.
The 61X cylinder has better port timing for the Superjet than other 701 cylinders. (Only one other, actually).
Epoxied cases can be taken apart just fine. This is not done for higher compression motors.
Voids in the top case half are filled in with epoxy so that the intake runners on the cases can be ported. Without epoxy, the porting results in penetrating those voids, making the cases useless. So you epoxy it to prevent a break-through.
Then there is also epoxying the fingers in the intakes. That's for reducing the volume of the intakes and increasing flow velocity.