Well that was a fast turn around. Dropped the Mustang off on Friday and it was ready to collect on Tuesday. Turns out there was a few things wrong with the C4 but the reason I lost reverse was due to a disintegrated gasket. Everything was well worn in there as well and some vacuum module was leaking ATF into the Engine. :O So he changed everything that was changeable including all the bushings etc. £1600 is not bad I guess??
Now on the market so hopefully it sells so I can get another toy in the UK.