RB VS B Blocks

i just read in that there is TWO 383 motors. a B block and RB block. when was the RB 383 made? it has a 4.030 bore and3.750 stroke compared to the B 383 with a 4.250 bore and 3.380 stroke. weird. and yes the 400 4 barrels had "better" cranks. i only have 2 4 barrel cranks or else i would visually compare. the book says better casting under notes for 400 4 barrel cranks, yet says suitable for mild hop ups. everything else ive read says cast cranks can handle ALOT in these others yet the "better" 4 barrel states only good for mild hop ups? fiiiiishy