I always feel people should start with gears and exhaust since basically every mod need those two things to get best results.
Using 3.55:1 geared 360 as a de facto standard. And keep in mind that most 3.55 geared 360 are way under geared if maximum straight line performance is your desire.
Not that you have to build your engine to keep up with a 360 of similar hp but it's a good basis to compare. 318 will make about 50 lbs-ft less than a 360 and peak 600 ish rpms higher than a similar hp 360 which means at any given mph your 318 has to turn 600 rpms more to compare . So your gonna need more gear than the average 360. A quick gorilla math is for every 20 ish cid is equal to a gear step. So your 42 under a 360 so to equal a 3.55/360 you need 3.91 at least. And if you don't want to go that high that's when you can go with a combo of lower 1st and 2nd gears in the tranny and 3.55 which will give you the similar acceleration as 3.91 in 1st, 3.73 in 2nd and obviously 3.55 in 3rd.
As for heads the stock ones are a huge cork with that cam. Down the road after the gears and exhaust heads would be my next up grade. EQ'S are Engine Quest are designed to be magnum replacement heads but are stronger and flow a lot better. Will really allow your engine to breathe and probably add another 1000 rpm to your powerband without effects down low to much. And have closed chambers which will help with your cr which is probably lower than you think if it wasn't measured. Why do you think you have 9:1 what pistons are you running any milling or decking done and which head gaskets ??