i would like to add a sort of disclaimer, that ive only built small blocks and imports...never a big block, but ill lend as much advice as i can...
the benefit to stroking the motor is that by altering the travel distance of the pistons in the cylinders, you increase the engine volume.
for instance, i am currently running a 340 30 over, which comes to 346 cubic inches with a stroke of 3.58 inches, and a bore of 4.070. i have acquired a 360 crankshaft cut to fit a 340 block, and with the 360 rods (that are 6.123 inches, like the 340), and with the 3.31 inch stroke, it makes the 340 come out to something like 378, i believe. the newest mopar performance catalog has a full list of various outcomes for every engine, with different strokes. i believe that the 360 crank in a 340 comes to 372, and with the 30 over, its 378, but i may be off by a few cubic inches on that...and i dont have my book here.
the downfall to stroking is that you have to often have the bottom of the cylinders machined or "notched" to have clearance for the extra movement of the rods. also, with a shortened stroke, you turn more RPMs, so you will want a better set of rods, if youre going to twist the motor hard.