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Building a motor for spray and one for boost = two separate builds. Spray loves compression, boost, not so much. Boost makes it's own compression so to speak.
If you're building a motor for spray, build a forged 383 with 11.5:1 cr. Spray as much as you want. Start at 200. Go up from there.
One thing to think about. If you plan on building a big time spray motor. It'll cost over $2000 for the proper nitrous set-up. It'll be cheaper than a blower, but you'll always be wondering if it's working properly.