Minus the turbo, 400 hp is reachable at the engine with bolt-ons but you'll be pushing the limits on fuel and compression and could be done for around $5000 for the conversion if you two do the work. That would be about 320-330 RWHP. With the base engine and the STS system your 400 rwhp goal will be reachable and your costs will be about $9000 since you won't have to do so much engine work. I would not exceed the base 5 lbs of boost if you run the stock LQ4. If you can put some lower compression forged pistons in then you can run your boost up to 10 lbs and end up with 500 hp of drive train breaking force for right around $10,000. The T76 upgrade, intercooler, and methanol are highly recommended.

I haven't done the turbo update to mine yet but have done 2 ls1 conversions in 92 and 93 C1500s. The rest of my opinions are just that based on other's data and my observations at dyno days.