Good Cam for 318

Like anything it depends on your budget. I have run Summit brand SUM-6901 and their SUM-1789
in a 273 and 318 and was happy with how well the engines performed.
Of course if budget is on the high side the cams from Howards and Hughes are very good.
The Whiplash cam is designed for a stock lower compression engine such as the 318.It is a good one.
Also remember there are many variables as what the plan is for the cars usage.Meaning Street/Drag,Autocross or a daily driver.
Do you know the rear axle ratio ? That also is a variable when you choose.
EDIT; I just went back and re-read your post. If any cam change is happening,you will have to pull the heads
You "can" change valve springs while the heads are still on but.. A cam change without matching valve springs is a moot point.