Hi Nemesis,
The late, lamented, Paul Freshney, previous Editor of Model Boats magazine, built a 1:12 scale Manfred Seivers Mersey kit (23 inches long) and shared the build details with me.
He fitted Turnigy D2822/17 1100 KV motors which he said gave good performance and that would be good enough for me.
Not sure if these motors are still available but you should be able to find equivalents.
Cheers,
Colin