Hi
The current model Gainsborough has left hand inlets however itis not a direct replacement.
Unfortunately there is nothing that is a direct swap.
However....... Triton has recently brought out the T80Z this shower has been designed round being a retrofit unit (Tritons word not mine!)
The pipe work can be brought in from almost any position and there is a reasonable amount of space for cable entry from most positions.
Here is the link.
http://www.showerdoc.com/new-showers/triton/electric-showers/ZTRITO-SP8008ZUFIT-Triton-T80Z---8-5kW-(White-Chrome)
See Video at the foot of the page
George
If the existing wiring was installed correctly then you shouldn’t have a problem.
You will need a 40amp fuse/breaker
Here is a chart so you can check.