I've only heard 'as like as not' on the rare occasion. The common form I hear and read all the time is 'as likely as not' (likely, not like) 'as likely as not' *can* mean just a 50-50 chance, but this isn't the usual use of the expression in my part of the English speaking world. Where I am, 'as likely as not' almost always means 'probably' or 'very probably'. (ie always more than 50% probability) Example. "I'll as likely as not be at the party" spoken here means I'll likely/probably be at the party. I think I'll be there ... but I'm not certain.

"As like as not" suggests roughly even odds between two possible outcomes; neither one is more likely than the other one.