Usual recommended 6.5 mods - for RHD conversion

Hi everyone,

I have been reading the forums on the 6.5 Diesel and found some information.
If it wasn't for the Right Hand Drive conversion I probably would just buy a heath Stage 1 or 2 performance kit.
However, when the conversion was done i 1996 a custom manifold was manufactured. This include crossover pipe and down pipe on the opposite side of the engine. The down pipe seems to end in the same location as the original down pipe would have ended. There is no Cat, just a straight pipe back to the original muffler. Every modified pipe is mandrel bent.
So here are some questions:

Exhaust (Sound)
Most forums recommend a new down pipe and crossover pipe. Since mine already are mandrel bent I'm leaning towards keeping that as is and just replace exhaust from after the down pipe and out. What is likely to work and sound best of 4" + resonator or 5" + resonator? Other options?

Heath Max E Tork & Turbo-Master kit
Turbo seems to be stock, so expect heath turbo master to fit. What about programming. Is that related to exhaust flow or will their "normal" programming work?

Turbo whistle
Would like to hear the turbo. Will that change with the above

Gauges
Planning to get Boost and Pyro gauge.
Whats the best range?. Was thinking 15PSI Boost and 1300 Pyro