After screwing around all day thinking it was something not registering properly with the plugins installer, I ended up downloading the trial for 15.5 and installing it just local on my laptop since we are on 15.0 currently. From there I went to the crm integration section and found what the documentation was indicating for "Available integrations" and had it download the Dynamics one I was looking for, searched for the zip in the local server install directory and then copied the zip up to the real server. Would have saved some frustration if the download was just available somewhere and information not scattered across many blog posts on the 3cx page.
Frustration was quickly dissipated after I realized how nicely this is implemented, the zip is just an uncompiled c# project which is compiled client side in the 3cx app. I've already added to the zip a bit with some things like adding a note in the description field to indicate the contact was created by 3cx integration. I have plans to create a case/opportunity automatically and go to that if the contact already exists. This is really great stuff. Has anyone else made their own adjustments to the MS Dynamics integration?