318's are easy really, just like with any build. 4 barrel, dual exhaust, and advance curve first especially if you are on a low budget. Those 3 can be done in any order or all at once. May be Headers next. They will help but not make a huge difference until you go to the next step which I would recommend you do all at once. Cam, converter, and gears. You may need them all. Most 318's have around 9/1 compression so pistons aren't at the front of that list unless you are building one and need new slugs anyway. Aluminum heads may help anytime along the way but more after the new cam. You can add roller rockers but that all depends on the cam and they won't bump you to the next level on the dyno charts. Lots of things you can do and add. Some make power and some don't make a lot of difference. Just use a little common sense. And so you don't have to buy better parts at the next step, Choose the major components carefully. Like, a LD4B and a 600 cfm carb will work well on a stocker but after the big cam, aluminum heads, 4000 stall converter, and 4.10's, you might need something bigger and better.