Actually, it would be limited to 230kbps (That's as fast as LocalTalk goes without a very rare hardware clocking device.)
And I've been trying, and have as yet been unable to get TCP/IP to work over LocalTalk. (I want to have my Classic on the Internet without using an external adaptor.)
That said, I do have a wonderful device called an 'EtherSCSI'. It plugs into the SCSI port, and gives you Ethernet. It works on any Mac from the Plus to the beige G3 (I suppose it would even work on later Macs with an add-in SCSI card,) and there are drivers that work in System 6 through OS 9. (I use one to get my SE/30 online, and another for my PowerBook Duo 2300c.) They can be found on eBay reasonably cheaply. (The most common is the Asanté EN/SC)