Hello, I see you need a website in mangento from an opencart site. We have experience with both of this platform; you can look at our portfolio for past work done. As you rightly said, the site you are trying to mimic runs on mangento, we will be able to deliver this work depending on how much product you have in like 20 days. Our team will look for the theme or a similar theme and transfer your opencart site to this new team..
You can contact us to discuss further.
Regards,
Aish