Not sure about K member or motor mount issues if they are converting from a 4 or a 6 cyl to the 5.0 but the IIs did come with 302s in the last few years so it will fit. Probably need a different oil pan, swap the front cover for one with a mechanical fuel pump boss and change the water pump, unless they are keeping the serpentine set up but the long block will fit.
Thanks,
She just asked if it would fit, so I told her I would check in to it for her.
She said the mechanic told her to find a 302 / 5.0. So I would assume that's what was in the car originally.
Yes it will fit. As stated they came with 302's. Now it is probably more work then it is worth to retain the fuel injection but a nice dual plane intake and a 600 or 650 carb would work well on it.
It'll fit but the oil pan needs to be changed. The Mustang II's had the front sump pan if I'm not mistaken. Also, the later model engine has the reverse flow cooling system so if she's going to install it in the Mustang II, she may have to keep the serpentine belt system on it or change the water pump to the standard flow unit, so that she can keep her belt and pulley system for the accessories. Also, don't let her forget about changing the front cover.