Seriously, just buy a good CRT. Stop fooling around with all this line doubler crap
I still have 3 Commodore era monitors I use for my older console gaming. In fact, I like to have my wii hooked up to it because I get the best looking emulators running that way. (going to point out while I have some consoles, I don't have them all, so emulate I must)
On top of this, at least in my city, you can get a big ass free CRT TV for free, all you have to do is pick it up. Check Craigslist free section.
Trying to use old consoles on modern TV's is silly, as they don't scale well at all. Even the Wii, which does 640x480p looks crappy on a 1080p TV.