I built several 431's (383 based) and 451 B's long before they were cool and long before they were overshadowed by the (now more easily affordable) 496-511; I think of them more as lighter (both in weight and rotating mass) and more compact 440 where everything seems to work just a little bit better. If you already have a 440 RB in a B/E body, I think nowadays the couple extra $100 it cost to machine the crank for a 451B could probably better invested in (in terms of more HP per $$) in improving your cylinder head flow. Simply stated, a 440RB is still a very formidable motor and when you go with aftermarket rods and lighter pistons for either build anyway (which 20yrs ago was seldom used in the apples to apples 451RB vs 451B build comparisons back then) 20 yrs ago, a 4.25" stroker crank was at least 1200-1500 so not many 511's were running around on the street....so when you take those considerations into account I think today the 451B's 'real world' advantage diminishes quite a bit. Of course I'm the first to say that the 451 is still a great motor....but with todays' affordable stroker cranks vs machining the mains CW's and sometimes opting for an offset grind 3.90/ 2.200 rods) on a 40yr old crank, it's much harder to make the case for not doing a 4.15-4.30" 2.20 journal 496-511-517; compared to a 451 it's like getting more than a whole extra 440 cylinder's worth of cubes/power and torque for really (as pistons and rods are a wash) not much more coin.