In stock form,a 396 has way more potential then a 400 smallblock.The worst stock 396 oval port heads ever made with stock little 2.07"intake valves and no port work with just a 3 angle valvejob will match or outflow even the best 23 degree head smallblock aftermarket racing heads.Bigblock bottom ends have way stronger components,and there are a few other good features.The bigblock has a larger diameter camshaft core,so most bigblock cams cam withstand more lift,and bigblocks come stock with 1.7:1 rockers,so you can get even more lift from that.In reality,even the mildest factory performance bigblock cams had .550" lift.The 396 has a better rod ratio because the stock rods are 6.135" long which is longer then almost any aftermarket 400 rod setup being offered in kit form,and the 396 stuff is stock.You can build a 396 with a stock 2 bolt main block,stock crank,stock rods with good bolts,stock replacemnt performance pistons,a stock GM camshaft{L78 solid lifter 396 cam would be real strong}with stock unported closed chamber heads with no porting,just a 3 angle valve job,stock rocker arms,pushrods,lifters and valvesprings,a performenr rpm intake,headers,and an 850 double pumper,and have a 500 hp engine that you can drive every day and be built with mostly stock parts,and shouldnt cost more then about 3 grand to build.The next idea is to not build a 396,but build a 454.You can find more 454's then 396's,and they come with even better stock heads,and they are externally the same,so you can dress it to be a 396 and nobody would know the differance.With a 468{.060" overbore}with stock heads with a good valve job,9.5:1 compression,and a mild cam such as a 280 degree Isky Mega cam,you can build an 11 second engine that will run on pump gas and not even sound radical.Add a 125 shot to it,and even the most mundane 2 bolt main cast crank 454 will be a 10 second beast.With aftermarket heads and a race cam you would be hard pressed not to make over 600 hp with either a 396 or 454,and that is with basically off the shelf parts.Good luck.