I have owned, raced and built both, the low deck 400 blocks might be 5 lbs lighter than a 440 block, maybe not depending on each block The cold weather extra thick main web 400 weigh more than a standard 440 block I had to weigh 4 or more of each size bloxcks to find that out for myself due to the urban myth spread on here about the 400 blocks blocks weighing from 20 to 40 lbs lighter than a 440 block, thats BS I have seen several 440 motor split the main webs, especially between the #1 and # 3 cylinders I have not seen that in a low deck so far I have seen both blocks split cylinders so the choice is yours to make My pump gas 518 low deck stroker made 775 HP on Oregon pump gas last month on a DTS engine dyno, that motor has a set of CNC ported 440-1 heads on it. My 527 C.I. (440 block)high deck bracket motor with 12.8 to 1 compression and a little more camshaft( low deck is 260@.050 int.,266 at .050 EX with .700 lift, the high deck cam is 275 @.050 Int. and 282@.050 EX, similar lift) made the same amount of power on the same dyno last year with the same carb. using 110 octane race gas The bracket motor has a set of indy SR heads that are M.W. intake port sizes from Indy