Actually it's the Plus that has the tilt back. The SE straightened it out so that the skirt around the base uniformly hid the case joint at crisp 90 degree angles. It wasn't needed in the SE as there is no front connection for the keyboard that needed direct access to the logicboard, which does not make it all the way to the front of the case in the Plus.
I can't think of an easier fix than to cut out the rear connector panel indent on the Plus and replace it with the one from the SE. Just paint that section black to hide the work, since it is indented anyway. Don't worry about reworking the entire case.
Also, you mention wanting the top vent of the Plus. But you also mention running a hard drive. I hope you are not planning to run your SE with a hard drive, but without a fan. If so, you should really consider going with an SD solution as the hard drive will really overheat the ability of the convection cooled Plus case. If not you will obviously have to relocate the SE fan.