I'm not a big fan of 347 or bigger budget small blocks. I would say stay in the 302-333 ci range, work over some 289 heads, 11-1 comp, RPM intake, big ass carb, cam that peaks somewhere around 7500-8000 RPMs. Then put it on some gas.
also recommended for 400 hp:
headers, e fan, ignition, decent rear end, locker or spool, sub frame work, probably air bags, brakes, tires, clutch, decent gauges, AND mufflers and more
why air bags?
Seth Stewart '04
2000 Suburban DD
1995 F150 SAS - Needs more work to sell
1998 GMC pickup - sold
2003 Yukon XL - wrecked/motor donor
1975 Scout - TBD
1976 Scout - parts truck
1972 IH 1310 dually - TBD
196? Scout 800 - 302 roller