You'll need headers to run the stock pulley.
3.4 on high comp requires an ic or cam but will make high 200's at the wheels.
Hd diff is worthless.
Your clutch packs, input shaft and chain set are the weakest points right now. They will all fail in the high 200's, low 300's. Regardless of power adder choice.
Top swap results in better driveability than an l67/trans swap due to having more power out of boost (compression) as well as better gears.
You wont be able to run as much boost nor as small a pulley but youll make more power compared to a low comp engine on the same pulley/ boost level.
This keeps the m90 happy as it is a terrible power adder that only becomes less efficient the more you modify. Ie smaller pulley, more boost.
