There is no question that a big inch- or any inch custom engine by a good builder with all the right pieces is a sweet set-up- although a little spendy. Resale can be tough if you don't stick with prominent names, many of which are familiar to this board.
Don't overlook that the 454 mag EFI is the same long block as merc used for the 525SC. Several reputable board engine guys and columnists have commented that the 525SC can easily be upgraded to a reliable 600 HP with intercooling, more boost and tuning. The Whipple / 454magefi is at 625, not a far reach, no doubt made safer, reliable and attainable thru the benefits of intercooling, EFI, computer controls, knock sensors, EGT monitoring etc.
I'm not trying to beat a dead horse- many are unaware of the connection between the 454mag and the 525SC and this info is intended to help with informed decisions.