Since you are clearly new to QNX I can understand that you are confused about all this, however you what you are saying and asking makes no sense. That is why we can’t help you.
If QNX 4.25 is the target platform for a student project, why don’t you have QNX 4 available to you? This is all very strange since QNX 4 is not available for download, nor can it be used for free for any period of time. The opposite is true for QNX 6. While the hardware support for QNX| 4 is not bad, the support for QNX 6 is much better. If QNX 4.25 is not available to you, then there is no way you can build a QNX 4.25 target. You might just as well ask how you can build a Windows CE or Linux target using Momentics. The migration kit has one purpose, not the one you are hoping for. It helps people who have QNX 4 source code port it to QNX 6. It doesn’t do any emulation. It tells you what QNX 4 routines are available under QNX 6, and which are not, and for the ones that are not, what you need to do to change them.