A T3/T4 turbo is a hybrid using a T3 turbine and a T4 compressor. A T3 uses a T3 turbine and T3 compressor.

.48 is the aspect ratio(A/R) or the turbine housing. This is an over-generalization, but a lower A/R will mean quicker spool with a lower "ceiling", while a larger A/R will mean slower spool with more top end power.