I believe the RAF Mk 1 had the Solar Titan APU installed, but the one you have may not be that model.
Note: hillberg says that it may be fitted to "Combine Harvesters" (International Harvister-Hamelton sustrand-Turbo mach.) = International Harvester - Hamilton-Sunstrand Turbine Machines. A quick Google for "Solar T62" reveals that some potentially relevant Manuals are available for purchase/download.
So, you could try an agricultural machinery supplier in UK or EU for spares/breakdown diagrams or perhaps just buy one.
Happy hunting - and let us know when you get your beast airborne?