I moved a boa into a boaphile 421D when she was about 2 FT and 100 grams. No problems with her.
I just moved my second small boa into another boaphile today. He's about 2.5 FT 200 grams...
so I'm hoping it goes as smoothly for this guy as it did for my little girl.

I also put a boa in another 421D, but she was 5ish when I got her, so she wasn't that small.