Migrating from joomla to wordpress

Hello, I have 2 questions regarding migrating an existing site. I built a site years ago using joomla as the cms and it ranks number 1 in my city on google so I don’t want to jeopardize that ranking. My issues are first I want to migrate it over to wordpress and I was curious what you all think that might do with the google rankings. And, second it is on a .net domain and I now have both the .net and .com domains. I would like to install it on the .com but I am afraid google will not recognize it as the same site. Should I just rebuild it on .net and forward the .com? Any input would be appreciated. Thanks.