Might as well chime in on a little something I found incorrect throughout this topic.
You guys have the injector sizes wrong.
After some flow tests the 84-86 injectors actually flow 850cc
In 1987 the went to a primary secondary setup instead of the back and forth setup they had before.
The primary on a 87+ is 550cc, and the secondary is 1025cc.
A decent little upgrade for 87+ cars to remove boost cut, and increase engine response a bit is to add a 1g eclipse turbo MAS.
86 widebodied starions were a ugly duckling of sorts. even with the 10,000k potenthisizer you still cant get past the 15lbs boost cut. It is possible to adapt a 1g mas to the 86 but it requires blocking off some of the unmetered air on the mas. It's a real pain in the butt, but does yeild good results.
I see a lot of people recommending 2,5inch exhaust. Personally, I would go 3. I have had no drawbacks, and dyno numbers seem to prove 3inch is the way to go. The whole key to a turbo setup is to have the backpressure on the exhaust side of the turbo less than the manifold side. if you are vise versa, then you are losing power. I've personally ran both, and must say the 3inch tends to breath a bit better up top. even on a slightly modded car.
there is a faq on starquestclub.com to upgrade the ignitor on a 86, and 87 to the better 88-89 box.
Get rid of the balance shafts to make a more reliable and responsive engine.
As for piston choices. THere are guys putting at least 334rwhp and roughly 387ftlbs of torque to the wheel on stockpistons, so I really dont see the need to go with forged for most applications.
The best aftermarket head is no a clearwater, or alabama, but a MARNEL head cast in spain. They will hold up to overheatings over and over without cracking. They also flow about 30cfm more than a stock head. Your other choice is to get a australian Manga head with a casting of I believe m8 or higher. For na, they also had a kidney based head on the last gen 4g54 made in australia. This would be a good canidate for a high comp na engine.
if you have the money, do yourself a favor and go with a magna mpi converted turbo g54b. You basically get about more hp off a stock starion setup, and 10x the throttle response, efficiency etc... You could easily lay down 300ftlbs of torque to the wheels with a stock starion turbo and mpi.
I saw some mention of a 4g63 and 4g64, they are great engines, but in the engine any turbo dohc setup will not yeild the low end of a starion. The big ol 2.6 is just as capabale as any of the other engines out there. We all know it comes down to money. There is no reliablity issues with a 2.6turbo engine running a marnel head. I've ran an entire drift season with my old 87 conquest with an 18g revving up to 8000rpms on a stock g54b bottom end with bsek. Overheated it many times and it still runs fine

With that being said, the 4g64 would be the next best turbo swap. If you can find a wideblock 4g64 out of a mitsubishi box van, or some early mighty max trucks, they will be wideblock, which uses the same bolt pattern as a starion g54b. After it is all said and done, you will be looking at at least the same chunk of change it would cost to swap in a starion mpi setup.
I've questioned using a na oil pump on a turbo engine, but if you guys are running them without any problems, that solves one of my problems

here are some dyno sheets of modded engines to get you an idea of what mods are gonna give you what powerband on a g54b.
http://www.starquestclub.com/forums/viewtopic.php?t=8890