This question comes up weekly and so we can all pass on info that is useful I took a few photos for perspective.
This will not fit in the JK rims without machining the centre of the JK rim to suit and then it will not be suitable as a spare for your JK... So what's the point?? You cannot simply get blank hubs drilled to suit a JK stud pattern!!
See the problem (that is also ignoring the step on the hub face to centre a Landcruiser rim as some don't have them).
You could get around this ILLEGALLY by using ford hubs with TJ-JK wheel spacers and might have enough depth to fix the backspace and hub dia issues.
Do so at your own risk and potential legal liability!!!!
As others have said, basically not worth your effort! Match rim size, ie all 17" and carry the one spare each for both car and trailer and a spare tyre carcass and learn to demount tyres if you are that remote.
Matt.