Hello Jack
I've changed them slightly, to make them more idiomatic:
1. Sorry it's taken me so long to get back to you. I was busy. ] I am getting back to you now. I was busy.
2. Sorry it's taken me so long to get back to you. I have been busy. ] I am getting back to you now. I was busy and I'm still busy.
3. Sorry it took me so long to get back to you. I was busy. ] I got back to you in the past. I was busy.
MrP