I still think it's better to just get another body- an MX or ME Super is very small and light. If you're worried about your back put it in a waist pack. A fanny pack will hold the combo.
The ME Super weighs less than a pound. The MX weighs barely more than a pound. Both are tiny. Both have big, beautiful viewfinders. As for lenses, the SMC Pentax is the SMC Takumar, just in K-mount. It costs about the same. The SMC Pentax-M is lighter and smaller, and still gives nice bokeh. Either will give full functionality, including AE on the ME Super if you want that. You can put a screw-mount Takumar onto any K-mount camera with an adapter, though you lose auto diaphragm, no worse than with the Nikon.
With all the options, why go to the trouble to hack a Pentax onto a Nikon? To save a pound of weight? Come on.
BTW, I've got an F3, and while its viewfinder is great, the Pentaxes are just as nice.