Hugh Le Fleming in the trusty old Ian Allan ABC - Coastal Passenger Ships - 1956 Edition (which uses LOA as stated in Introduction - unless marked otherwise!!) - lists -
Britannia - 238'
Bristol Queen - 258'
Cardiff Queen - 248'
Incidently - Width appears as 30' but have seen 59' quoted = which must be over Paddleboxes
Essentially = paint the Funnels and top section of hull white and bridge brown to represent wood and - more importantly - it will look like a Campbell steamer!!