I'm modelling the X-15 with the XLR-11 engine, X-15 with XLR-99 engine and the X-15A-2 (both in white and pink colour schemes. So far I have the XLR-11 variant complete and now working on the XLR-99 variant. Here is the X-15 (66670) with the XLR-11 engines.
I've added a basic hangar, so I can create rendered views with various pieces of equipment surrounding the X-15.
I've started on texturing the cockpit and whilst gathering information, I've found out there was very little space in there. This is the XLR-11 version of the cockpit.
Of course you'll need a B-52 to launch this manned missile:
Some preliminary work on the X-15A-2 (66671), including fuel tanks