You got some nice yard pickin down there. Since you are going Megasquirt you should change over to the DOHC to start with. The newest MS 2 extra code has the program for the Mitsu ignition in it, both the G63 and G72 are covered properly now.
The DOHC already has more power than you original goals to start with. Just port your intake adapter for the larger ports and let it go!

Cheers, Charlie
If It ain't broke, Modify it!
87 Montero turbo Converted back in Spring1989
95 Montero SR 3.8 DOHC Only one?
93 Pajero 3 door 6G75 Mivec with paddle shifted 5 speed
Then a Gen2 SR with full coil independent suspension.