Some background on the 451 "B". I think much of the success of the 451 combination was from articles in Chrysler Power magazine in the late 1980's.
They were putting turned down 440 cranks in with stock cast pistons milled for the compression height. Because of the shorter deck height the pistons weighed less than a 440 so the engines would RPM good and were cheap to build, considering no one wanted 400 blocks, they were much cheaper than buying a 440. One of the first failures was the piston pin pulling out of the stock cast piston at sustained high rpm. So custom (at the time) forged pistons were used and I think the custom pistons also allowed running the longer 440 rods. At this point 451 "B" had the same stroke and rod length (and about the same bore size as a 0.060" over 440), but with pistons that weighed about 1/2 as much as the 440 piston.
The lighter weight pistons also reduced the stress on the crank and rods. So at the time the big deal was the low cost of the 400 block and light weight pistons. The "B" engine may also have some strength advantages over the 440 "RB" with shorter cylinders they should be stiffer, the shorter deck height uses shorter pushrods (stiffer and weigh less),the smaller main bearing size reduces friction and allows more material in the main webbing and caps, but that's usually not a problem on a 440, but the difference is usually mentioned.
Another issue is the shorter deck height "B" engine at 9.98" compared to a 440 "RB" at 10.725" results in the "B" engine being slightly narrower so it fits easier in A-Body cars.
Anyhow, 500 HP is easy with decent flowing heads and a mild cam. With better heads, and some cam 600 HP is not too hard to make. 700+HP is possible with good aftermarket heads and a bigger roller cam, but at this level you will want a stronger than stock crank and rods, so larger strokers are usually built. The 500" "B" stroker with 4.15" crank still uses the longer 6.768" rods and a pretty short compression height piston requiring oil ring supports. This is a nice combination for a higher winding 7,000+ RPM engine. The 4.25" stroker 512" kits use a shorter rod, and are really nice for a street engine that does not need to spin 7,000 RPM.