You need to replace those files in the /webassist/ folder, not in the /installs/webassist folder. I think that is why you are still having the issue with the https:// redirect.
Copy all of the files from /install/webassist to /webassist and upload them and it should work properly.
I didn't add tax and shipping to the express checkout process... since you can change your shipping address on that page they may not be accurate, so adding them could be just as misleading as not.