Don't worry too much! I too made a Hauser but w/ a bolt-on neck, and I too had some problems with the neck angle, as it was just a bit backwards. Yes, a steel string is usually a bit backwards (nut going below the top) and classical is usually flat or a bit forward (nut going above the top). It is exactly as you said. Steel strings require quite high of a string height off the top while classicals require a low height off the top.
A bolt on and dovetail are very different but both allow you to shim the neck to get the correct neck angle, which in my case was flat. So with judicious use of shims you should be able to get the correct neck angle.
Make sure you can get somewhere close to these measurements:
12th fret: 3mm High E, 4mm Low E
String height off top of body: 9-11mm
You might need some planing of the fingerboard to get the correct measurements.
Regarding the 12th fret being passed the body join, I don't think it's too big of a deal. I think you will just have to put the bridge a tiny bit farther than where it was originally going to be. The difference will probably be not enough to move the bridge plate, I would think.