mild 8lb boosted 400 cam reccomendation

Mad Dart ought to be able to help point you in the right direction, but I think he spends most of his time in the SB tech area, or forced induction section. In either case, I'd suggest you call up a custom cam grinder and solicit some opinions from those who routinely run turbos. A 400 ci engine shouldn't have much trouble building exhaust pressure for a correctly sized turbine, but the cam will have a great deal to do with that. I think what you want to avoid though, is too much overlap...too much overlap allows exhaust pressure to bleed at lower rpms and that hurts your spool time. Have you checked out the turbo forums yet?? There are some pretty bright guys in there.

turboforums.com

Also check out forcedinductions.com...call them and speak to a fella named Jose, if he's still there.

I might be stating things you already know, but if you don't buy a correctly spec'd turbo, you'll have something that could either spool up fast and dies quickly on the top end, or takes forever to spool but exceeds your max engine speed efficiency. I'm going to guess by 70 trim you mean a 70mm impeller, but have you figured out what size turbine and A/R housing you want to run?