Fix the fuel bAlance problem FIRST.
It exists because you need more points of dispersal, not a different kind of turbo kit.
Add three YFA Carters on an Offenhauser adaptor, and put the air mix bewteen the carbs at two spots above cylinder 3 and 4. Problem solved.
Ak Miller totally knew what he was doing. He did what he did because for a 10 pound boost, a 1.68 boost ratio makes another 68 horspower easily with a stock 1.08 Motocraft carb. For a time, the whole kit was CARB legal if you kept the gasoline emissions gear on pre 1980 engines, and most of his other kits were Blow Through Propane or Draw Through Gasoline with a Holley 4bbl.
Ak Miller basically looked at making sure the stock pistons wouldn't let go...his systems were all based on that one fact..with a stock engine, what can I add here?.
The answer? About the same as a good nitrous kit with perfect Excess fuel....about 90 to around 135 hp. He targeted about 68 hp increae on his 200's and 250's, and about the same on a stock 300.
If its a stock 3.3 automatic in a 2600 pound car with a 256 degree cam, you can add about 18 pounds of boost if you can get the fuel pump and power valve like Does10S[/b had on his older incarnation of Kellys Falcon turbo]....and you'll get a reliable 14.5 second quarter mile or better. For that boost ratio, thats 220 hp at the flywheel, up from about 85 to 94 hp net stock. If you wanna kill it, equal to about 300 hp net at the flywheel if its got over 20 pounds of boost. The little six can do crazy amounts of boost. Then it donates due to lean or rich fuel, which over loads the rings, overspeeds the engine, and it blows a head gasket or takes out a ring land. Or maybee a rod, although that's very hard to do with the 200 because its a lot stronger than a 250.
The way to stop making your 200 a pile under boost is to just add three Carter YFA's without a staged throttle. This is what you cal a postive way to create Excess Fuel Factor to avoid lean outs.
Add a Ak Miller style 270/290 cam withabout 470 thou lift, and if its a rebuld, have the machinist hone out the bores to a proper cylinder wall roughness measured by a proper lazer profilometer. If the shop doesnt have one, and they can't give you the included angle, the Rpk, Rk and Rvk readings, then you've got the wrong shop. Run away, and never return to it. All that old average Ra roughness count crap has ruined more engines with 5/64 compression and 3/16 oil rings under load because of what happens to the oil retaining part of the cylinder wall under boost. It destroys it if the wall texture is stock, and the oil evaporates. The crook air fuel ratios do the rest. Blow or draw through won't help or hurt, its about fuel wetting the whistle of those six cylinders properly.
The plug readings will tell you plenty, but the old timers like Ak Miller were very conservative, and he got sales to ensure he kept the engines on song under boost. If you llok at any article written about the late great Ak Miller by the late Jay Storer, you'll see that the engines were designed around the application, and that they were quite conservative, with ductile iron rings, or chromium if it was dual fuel and you could run them in. Things have changed. Metric ring packs are low tension, and require a much smoother finish with plaueau honing to a target Rpk, Rk and Rvk reading. An average Ra reading is useless for a modern rebuit Old 200 Turbo.
A good US made piston by Silvolite for the Australian 200 or 250 six will work great in a Turbo 200.