P2PK and send to IP are two different concepts.
P2PK is simply Pay to Public key which was changed into Pay to Public key Hash later on. in the early versions your output script was the public key but now we are including the RIPEMD160(SHA256(pubkey)) instead.
Pay to IP is not a script type, it was more like a "communication option" and a client feature rather than being a bitcoin feature. meaning your client opened up a socket on a certain IP:Port and then tried connecting, if it succeeded with the handshake then it sent a different message asking for a public key/address so that it can make payment to it. the next step was the same as having the public key already and sending to it.
@OP: are you trying to "dig" the wallet for altcoins?
Any idea why they stopped doing that? I was thinking it might have been down to the use of tor but now I'm not sure if it was more of a request style system. Maybe it's a privacy thing?
there was no way to be sure the public key sent by the receiving node was not a middle-man. More info in this thread.
Ah yes of course, because nothing is encrypted - silly me!