It all depends which 400 you have- if it's the L78 400 with a 500557 400 block and 6x-8 heads, you can forget about stroking it. This block is the notorious thinwall casting and can crack at the main cap dowels (yes- I've pulled apart more than one and seen it). You can roll the dice and use it, but IMO it's a waste of hard-earned money-stick a mild cam in it and be done, you can make up to 400 hp with it (and better heads), but it's inherently weak. Look for a 481988 400 block and use that instead.
The W72 OTOH can be stroked with the stock 6x-4 heads and make 450 hp/500 lb-ft even with stock heads- careful cam selection, carb and ignition tuning will make it a potent build that appears completely stock, but has double the factory output.
Geno