Granted that I have posted most of the info on another board but I though I'd add some of the info here just in case.
The stock turbo for the draw through system is inadequate to say the least. It's completely backwards to the way most designs that work well. The stock turbo flows roughly 350 CFM where the updated design flows 675 CFM.
I started looking at the stock turbo and if there were any upgrades out there. There are none that will not increase lag but they will work better at higher RPM's. To decrease the spool time on the turbo you need to completely redesign it.
It's not near as hard as some would believe.
What I did is look at the 301 TTA turbo and the 86-87 design. I was lucky enough to get the turbo maps from Garrett so I could compare them. With the large exducer (exhaust side) and small inducer (intake side) the engine just doesn't flow enough to spool the turbo properly. What I ended up with is using the exducer off the 86-87 turbo and the inducer off the 301 TTA.
Here are the maps for comparison so you can get a better idea of what I'm talking about. The are posted using the 83 turbo, 86-87 turbo, and then the TTA turbo.