"Also if the Island Line does receive 1973 Tube Stock, then wouldnt each unit be formed of three carriages due to the location of the air compressor in the Trailer vehicle and the position of the motors are in the Driving Motor vehicles?"
No, they will do the same as they did with the 1938 stock and move the compressors under the motor coaches.
For the person who suggested the 139s, get real. They have nothing like the required capacity, and really are not suited to a route of that length. Increased frequency is not an option unless the route is double tracked, and to be honest by the time that amount of money is spent you might as well just rebuilt the Ryde tunnel and get some proper trains not toy trains.
To be honest, my "money is no object" proposal for the Island Line would involve conversion to mainline stock (probably ex-SWT 455s) south of Ryde St Johns, including capacity enchancements, line speed improvements and re-opening (at least Ventnor, if not other routes). Esplanade to St Johns, including the infamous tunnel, would close, and Esplanade to Pier head would be replaced by a Tramway which would then run down to St Johns and other destinations. My other solution would be the same, but would have the trams joining the IOWR formation at St Johns, with the option of some street running at other places. For now though, old tube stock seems to do the job nicely.