It probably depends on the make of your DVD player.
As you can probably see from my name, I am a Canadian, who lives in the UK in the winter, and I play NTSC tapes and DVD's all the time.
I just put the NTSC DVDs or video tapes into the players, and away they go automatically.
As you've made your DVD multi-region, that's all you should have do to get a picture.
My TV will also switch to NTSC, which I have never done, but it still plays NTSC DVDs and even shows video from my cam-corder when I plug it in.