351 WINDSOR HEADS ON A 302, possible?

They bolt right on but I think the 351 heads are drilled for larger head bolts.

the heads will bolt up no prob, you just have to get what is called "head bolt bushings." these things will take up the slack of the 1/2" size bolt holes that the 351 takes cause a 302 uses 7/16 bolts. they just go into the head before you put the bolts in. sometimes they kinda have to be pressed in, i just let the bolt press it in while tightening them up.
for the valve train, that depends on what heads you are using, stock pedastal style or stud mount. and you will then also have to check for proper pushrod length as well.