I don't know whether the HRS will be restored or whether 558 will use MFS for the flight instruments.
If they're not, the aircraft will need to be modified from its original configuration. Anything as radical as a new attitude reference or fuel quantity indicating system would require a major modification from an approved design organization. Capable as they are, is that kind of modification within the scope of Marshalls' design approval? British Aerospace would certainly be OK, but I doubt if they are willing or able to commit such a high level of resources to the project.
My point was, the availability of (often small and seemingly insignificant) spare parts is the critical factor that will determine the cost of getting and keeping the aircraft airworthy. Original Equipment Manufacturers' (OEM) goodwill is one thing but they are not charities and must consider their shareholders views.
My own experience of civilian maintenance and airworthiness matters leads me to believe that this project is ill-fated. The UKCAA are one thing, but EASA looms larger on the horizon and it is EASA's rules that will apply by the time 558's overhaul is completed. So far, EASA have shown an entirely different view to the UKCAA's regarding aircraft preservation and "Permit to Fly" operations. Meanwhile the future of 'Sally B'
remains under threat due to new EU insurance regulations based on aircraft weight. Vulcans, of course, weigh very much more than B17s.
I'd much rather see at least one Vulcan properly preserved in good condition for posterity, than have the owners go broke and leave the aircraft to rot. It isn't the start-up costs that put the majority of new small businesses out of business, its under-estimating operating costs and over-estimating revenue.
Nevertheless, as an old Vulcan mender, I really do hope that I'm proved wrong.