The 400 is decent, but like 73RS said, the rod/stroke ratio could be better.

I'm sure you've heard of Canadian High Performance in BC? Its where I buy all my parts from, theyre cheap and its in Canada - Check them out: www.hi-performance.com - 6 inch rods are under $400 CDN for the forged street ones.

Even without the 6 inch rod set-up, the 400 SBC is pretty damn sweet. My buddy was running 12.20's in a 3000 lb '69 Camaro chasis with a 406 (.030 over) 5.7" rod, stock crank, 10:1 compression forged pistons, ARP fasteners throughout, Crane mechanical cam, ported Bow-tie heads (stage 2), Victor Jr intake, Holley 750 Dble pumper, and get this........ Points ignition! I tried making him convert to something from this decade, but he seemed to get his jollies on running points and being in the low 12's.

Mind you, he did have 4.10's in the diff, a built TH350, and a 3800rpm stall..... But the car was still relativley "budget" and he could run low 12's all day long.

Don't forget that the 400 is a siamesed block (no cooling passages between the cylinders), so this means you either need specific 400 head gaskets, or you'll need to add "steam holes" into the standard SBC head gasket like they came stock for the 400 from GM.
A bigger and better radiator will help (dont forget the shroud), as well as an aftermarket water pump and a good fan.