318 and which cam?

I'm trying to get some more thump out of my 318. I'm currently running stock bottom end/heads with a edelbrock intake/600cfm carb and a set of Dougs and a 420 cam.

The options I'm looking at are a 454 or possibly a 480 and changing springs in the heads.

Curious if anyone can chime in on some suggestions. I'm on a budget but know someone else out there in my situation has probably gotten some good results?

Thanks in advance