Over at Network 54 the 335 forum, I have read past posts and said that .030" over was fine. However, if you do decided to go more than that it was suggested that you need to have the block sonic checked. I hope this answers your question.
It would be wise to have it sonic checked BEFORE you do any cylinder boring!
Clevelands are generally pretty thin in the cyl. wall thickness area.
.030 over is the absolute max on the street, without using block filler.
It's a pretty commonly held belief that .030 is the most that a Cleveland can be safely bored without sonic testing. I e-mailed Keith Craft Racing and asked him about this a few weeks ago and he indicated that if the block is partially filled that sonic testing probably isn't necessary. I guess it depends in part on how cautious you are with your engine project and how hard you're going to push it. Best wishes!