Originally Posted by
NutLoose
PS853 has a Shack engine but has had the gearbox at the front modded with a firefly unit if memory serves me correctly, to convert it to a single prop, it also had other mods like part of the rear casing machined down and the lifting eyes on the rockers also cut down so it would fit, when doing engine changes etc they have to swop the rocker covers so they have the lifting eyes.
There is an official Rolls-Royce modification to change the Griffon 58 from Shackleton configuration to fit in a Spitfire. The structural changes you mentioned are part of it but they also have to modify the carburettor settings to allow for a much lower idle rpm than the Shack ever used. I had the PDF that detailed the changes at one point but lost it somehow.