Don't forget the 400 is also 60+ lbs lighter than the RB, I have a 440 crank in my numbers matching '72 road runner and a 451" 12;1 compression 451 as a back up motor for my '70 Challenger that has been 9.60. That being said a business associate of mine needed a 400 short block gone (as in "FREE") after sitting around a few years since it was replaced with a 440 in his sons Charger, just pulled this thing down and it has never been apart, bearing match the date code of the block and being a '73 block should be a good candidate for a 512" stroker motor on pump gas for a street /strip car or back up to the back up for the race car..