The 302 is the same block as the 289 so it is a direct bolt in with the 289 mounts and uses the same accessory brackets, exhaust manifolds(or headers), etc. as the 289.
The 351W uses the same mounts as the 289 and you can use the same exhaust manifolds, BUT it will restrict the breathing considerably(performance in mind). I installed a 351W in my brothers '65 Mustang and it is tight, but there is sufficient clearance for plug changes, oil changes, and regular maintenance work. Hedman makes a set of headers for the 351W to '65 Mustang swap that I would reccomend. The shock tower spreading is only neccessary IF they have collapsed inward, not in order to fit the 351W. The 351C engine however will NOT fit without considerable work.
You will need all the accessory brackets from a 351W to mount up the alternator and power steering pump( if present) and line up your pulleys. The tightest clearance issues are between the steering gear and drivers exhaust manifold flange(the Hedman headers would solve) and the air cleaner to hood(351W is about 2" taller than the 289/302). That depends somewhat on your intake manifold choice.
Your front suspension needs to be in good shape since the 351W is about 70 pounds heavier than the 289, using an aluminum intake and heads would be beneficial to reduce weight.
If you are a fairly confident wrench, it is not bad as long as you have the TIME to think each change to stock thru BEFORE you take the step. As long as you have the tools, space and the TIME, it should be kinda fun IMO.
