Clarity MR caps for external crossover?

Make sure you keep your stock networks what your doing may not improve sound quality over Tannoys network

I'll get ZERO traction with this, but you may want to look into improving the inductor(s) in the bass circuit. This has the greatest need for power handling and may benefit from air cores. Stock inductors are probably iron/laminated/ferite cored. Matching DCR will gain power handling / headroom and not change the crossover point.
The other thing I see on 'stock' crossovers is incorrect placement of inductors.
Many are on the same plane and edge to edge where they interact....badly.
ALL coils should be at right angles to one another with as much spacing as reasonably possible. An external crossover maximizes these possibilities while keeping the capacitors safe the pressure changes inside an enclosure which breed microphonic effects.

Better to keep old network intact build new one compare the 2. How can you tell If its a real improvement unless you have a base to compare too. Best is to have 2 of the same model keep one stock make upgrades to the other compare measure changes. If not then its a true shot in the dark. For what I see some spending on over costly crossover parts they could afford this with ease.

The MR's have perfect synergy with Tannoy drivers.

For the values that CC does not make, split the value in half. Using unequal values, especially in series with the tweeter, will have a negative effect on spacial information.

As for the 200uf, I would consider ESA's though.

And I agree with Magfan in using an air core inductor for the LF circuit. Be sure to match the DCR withing 10, preferably 5% or you'll be sure to create undesired effects.

Does Tannoy make there own drivers? Do they use SEAS or Dynaudio?

I like the idea of comparing 2 complete crossovers......You can than basically A/B them and see which is superior.
Going at this piecemeal may drive even a stable person crazy.