Gents, to help clarify and hopefully ward off a bunfight here, I'll throw in my 2p worth.
As someone who was involved throughout the restoration phase of XH558, I can tell you that all avenues have been explored regarding the overhauling of the engines. Whilst yes, you are correct in assuming that the marine Olympus is similar to the Aero Olympus, and both share the 202 mark designation, the materials of which both are made differ considerably. As you can perhaps imagine, a marine engine is static, weight is of no consequence and it also has to deal with quite a corrosive environment, guzzling as it does over 240lb of salty sea air per second! Because of this, extensive use of Stainless Steel and other heavy materials are used in the compressors and casings of the marine version, along with other changer unique to that variant.
The Aero Olympus is a little different and obviously weight is a prime factor in the choice of materials, hence aluminium alloys and magnesium alloys feature heavily throughout.
Similar, yes. Identical, no.
Regardless of this, although Rolls-Wood (or RWG) have the approvals and licence from Rolls-Royce to overhaul the marine version, they do not have the requisite approval to overhaul the aero version, even if a supply of spares were available, which they are sadly not. There is no conspiracy theory here, please believe me when I say that all of these avenues were explored in the very early days, just as I'm sure you would hope them to have been.
The change in time between overhaul from an hours basis, to a cyclic basis was done upon the insistence of Rolls-Royce, the design authority, and was a condition of their continued support. During the RAF service of the Vulcan, the engines had a 2000 hour life between overhauls. R-R, in keeping with the way that their civil fleets are now managed, insisted upon a cyclic life of IIRC 1200 cycles (in this instance a cycle being one excursion from idle-max-idle) which, following some number crunching regarding average throttle movements per display and transit, worked out to around 1600 hours. To assist in trying to squeeze as much life as possible from this cyclic limit, Aerobytes fitted telemetry and engine monitoring software to work out the cycles and partial cycles as accurately as possible to ensure no cycle was wasted!
Aside from all of this is the major issue of safety. Please try and remember that these engines are certainly not the carefree handling and safe engines of today. They are of early 1950's vintage when failures were tolerated much more often than today as an unavoidable risk. Olympus engines suffered horribly throughout their life with rear bearing issues, and have RPM resonance bands that the engines cannot sit in for any length of time, lest they will vibrate theirselves to pieces! They are old engines that must be managed as such. Engine technology has come a long way, and safety must not be taken for granted. Rolls Royce are a company built upon a reputation of safety and reliability and make their money by selling safe, reliable engines to airlines to transport us all around the globe without fear of the engines spoiling our day, hence they will always err on the side of caution where old engines are in question. The fact that they have given as much support as they have, is pretty remarkable and is something for which we should be grateful, not critical.
Hopefully that's cleared up a couple of issues, I should add that I am in no way an official mouthpiece for Vulcan to the Sky, I was simply someone who was around at the time that these questions were being asked and was party to some of the answers!!
Flipflopman