Other option would be to scrap he vacuum system in favour an alternator on the vac pump pad for a standby electrical system to drive the standby attitude indicator and radio.
This would require an EASA major mod and a lot of work, If I could spread the certification cost across three or four aircraft it would make whole thing more attractive from a cost point of view............. any one interested?
Whose alternator and electric horizon would you be using?
The GAMI alternator is not yet certified. There are some from an outfit called B&C or something like that.
I keep half an eye out for this, to replace the KI-256 vac horizon, but would need an electric horizon which has the KI-256 features i.e. flight director and pitch/roll outputs for the autopilot. Not sure if anybody makes such a thing.