Well, first a touch of the 'theory of how constant-mesh gearboxes work' might help explain the tranny actions you're seeing a little:
The constant-mesh design requires gear rotation motion (here, either from the rear wheel when engine is off, or a running engine) in order to help the gear dogs on the shift-able gears to find their slots. The gearshift lever itself applies little actual force to do the shifting, so the well-oiled and spinning gears provide most of the motive force when changing gears. That's why this feels so weird when you're trying to do it by hand with the engine off. The shifter pawl gizmo(s) only partially turn the shift drum until a disengaged (and not yet aligned) dog(s) tries to enter the corresponding hole(s) in the mating gear, at which point that mating gear needs to be spinning to present the hole(s) to the dog(s) as they previous gear had holes and dogs in different locations from the one you're trying to engage with this shift. (Whew...)
OK, on to the problem:
if the (formerly broken) pressure plate's splines are not aligned with the clutch hub's splines, then tightening down the (4) bolts will not close the plate's stack. It is entirely possible (which is how the old one got broken) to do this on assembly. The misaligned pressure plate will still be 'open' by the thickness of about 1 clutch plate, so the symptoms will be like yours are: a slight drag in gear, but no power to the rear wheel, because there is just some light drag between the cork and steel plates. This is also how those pressure plates can get broken, as the springs will close almost completely when assembled and tightened this way, but no pressure is applied to the plates at all.
So...remove the 4 clutch bolts and lifter plate (again...) and then slightly separate the plates manually (so they are not stuck together), then try turning the pressure plate slightly by hand (by using its studs) for the rotation distance of about 1/2 of a spline. The pressure plate should then come loose in your hand and let you pull it toward you slightly (about 3mm) as it aligns with the hub's splines and all the teeth of the steel plates. Then leave it right there while installing the springs and lifter plate and 2 bolts lightly, then wiggle the lifter plate back & forth a little while finger-snugging those 2 bolts down to hold it all together. You'll be able to feel if the rear pressure plate's splines are staying engaged while doing this.
In the end of this little jiggle-and-snug routine, you will be able to start the 2 remaining bolts into their holes and they will be at least 8mm 'high' (disengaged) from their tightened-down position, indicating a correct alignment at the pressure plate. If instead you start to install the 2 remaining bolts and they only have about 3mm (1/8") of length sticking out prior to tightening them, the pressure plate is misaligned and is resting against the clutch plate splines instead of being engaged with them.
