Based on section 4 of the license, you need to:
keep original copyright comments
mark the files as changed (eg. modification copyright XXX XXXX)
keep the LICENSE file
keep the NOTICE file if it exists
It would make sense to leave in the readme that you have created a port.
Generally, this is called Multi-licensing when you want a particular product to have more than one condition. Any product can have more than a single license.
In Open Source it has its own term which is called dual-licensing, and its use-case is similar to that of the general team Multi-licensing, we do this when we want our open source project to have two ...
Your obligations when copying a file from an Apache v2 licensed project are the same, regardless of the license of the target project. You have to retain the license, copyrights and any additional attributions from the NOTICE file.
When the target project also uses the Apache v2 license, then you can merge the two NOTICE files and you only have to have a ...
Apache's position is that their v2.0 license is compatible with GPL v3.0 but only in the forward direction. That is, you can embed Apachev2-licensed software in GPL v3.0 licensed projects, but not the other way around.