I too had both blocks to chose from and I went with a 451" for a few reasons. One I really like how quick the 451" combo revs. It's literally like a chain saw. Also I was fighting for space( height) for my air cleaner. "B"combo's sit lower than "RB" COMBO'S, and slighly lower weight. Also I came across a good deal on a pair of Mopar stage 6 heads which I read are "happiest" on smaller CID combo's.
I had narrowed it down to either a 451" or a 512" RB.
Cost is about the same on most combo's . I got my kit from Muscle Motors. Look at 440 sources web site too.
With the price for all new lightweight, stronger parts , why bother with stock stuff? By the time you remachine your crank and rods , buy pistons, bearings, rings, balance it all.... your pretty close to an all new lighter weight, stronger, stroker kit .
If your looking for every last HP then maybe a 451" is not the best choice? I figured a 451" would get me into just as much trouble as a 512 would!
I can still fry the tires at will with the 451 so why build more motor than the car/chassis/tires will allow I figure? 500 HP from any BB combo is easy enough. How much can you actually use on a street car? Also remember a stout engine WILL find the weak points in the rest of your drivetrain....
If your willing to get rid of the power brakes with either a manual set up of hydroboost it opens up a lot more cam options for you!
Here is a link to my junk?...
http://www.cuda-challenger.com/cc/index.php?topic=78386.0http://www.440source.com/strokerkits.htmhttp://www.musclemotorsracing.com/stroker-category.html