Mario. I'm not sure if you still have the Mk 4. If you do is it possible to make a Mk 4 "mariocp" edition by repairing and modifying the Mk 4 to take the same mounts as the Mk 5 Morgan edition, plus the extra flex joint? In that case you could keep the new silencers in a box for future use. I imagine that at this point Morgan may be unlikely to supply any further warranty replacements.
Unless something has changed with the internals of the Mk 5 version the ECU should be OK with all the versions.