Encryption scheme with arbitrary length message Is the definition $\Pr[\operatorname{PrivK}_{\mathcal A,\Pi}^{eav}(n) = 1] \leq \frac{1}{2} + negl(n)$ still valid in case we have an encryption scheme  $\pi (Gen,Enc,Dec)$ with arbitrary length, and the adversary $\mathcal A$ is not outputting equal length messages?
As poncho already wrote in the comments, this isn't possible:


Basically the only way to hide the length of a message is to use a padding, which is long enough.
The adversary knows at least the encryption method and implicitly the length of the padding.
If you allow arbitrary messages, he can choose one message really short (e.g. 1 bit) and the other longer than the padding. If your encryption scheme allows arbitrary length messages, this must be possible, e.g. by a mode of operation (known from block ciphers)


You can't adapt the padding length after seeing the messages chosen by the attacker. Otherwise the information about the length might leak other information about the message again, and then you're going in circles.

edit: Oh, and again you might want to explain notation and security games in the question - even if it doesn't actually matter for this one. Writing down clear definitions might help you see problems on your own.