Tuning this engine for higher boost?

[GHOSTOWLGRID]

its a LG5 3.1L turbo v6 from a 1990 Pontiac Grand Prix McLaren.
I swapped it into a 1990 Chevy Beretta Indy.

This is the info on my engine:

http://www.v6z24.com/specs/31turbo

This is the tune file I found:
8f.xdf version 1.1 for Tunerpro Download Entry
89-90 Turbo Grand Prix 3.1 file

What is the best way to modify this for maxing out the turbo without losing efficiency?
How would I calculate the A/F ratios to do this?