Smoke,
Believe me, I would be the last one to dissuade you from building what you want.
I know how you feel - having an attachment to a particular cartridge for whatever reason.
I do agree though with the shortcomings of the 577/450.
One consideration in all of this, is that if you are going through all the expense and trials of building a double rifle, you may as well choose a cartridge that isn't going to add to the challenge. There is so much information out there on the 450 3&1/4 in BPE and NE loadings that it would be hard to argue with that choice.