My predictions.
Drifter Versas onto the 61.
4 Versas to Chester Le Street for the Lambton Worm.
Versas for the M2 / M3.
Some of the MPD displaced from the M2 / M3 to Deptford for Doxford Clipper.
547 was repainted because it was the oldest Doxford Clipper MPD.
36/36A might get MPD or Versas, but I'm not sure on that at the moment. But those are my guesses at the minute. A bit revised from what I posted on facebook as I didn't take into account of service changes.

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Right I've cracked it.

Someone mentioned that they could be putting Versas on the 39 to increase capacity. However to increase capacity on the route doesn't necessarily mean putting bigger buses on the route. It also explains why 547 has been repainted.

The reason 547 has been repainted as it's only a 25 seater vehicle where as 603 - 606 are 29 seaters.

Currently the 39 (using 603-6) has a capacity of 87 seats an hour.
Now if they put the Drifter Versas (39 Seats) on at the exsisting frequency then that would increase to 117 seats an hour.

However GNE is increasing the frequency to every 10 minutes between Sunderland and Doxford Park. Therefore needing more buses. The 53-Plate MPDs are ideal vehicles to be moved from the Street Shuttle as they are also 29 seaters. So the capacity between Sunderland and Doxford Park is now 174 seats an hour, which means a capacity increase of around 74%.

It also means the main street in Ryhope to Tunstall Green will have 14 buses an hour to Sunderland.