Bitcoin public key pre-0.6 length before hashing
is the buffer pre-hashing always 65 bytes long, 


yes


  since compressed keys were not supported?


they were not used by anybody. but there were no changes in client to "implement/support" them


  Or was it 64 bytes long (just &lt;256bit x>&lt;256bit y>) and there was no byte for the version prepended before hashing?


no. the client was written with openSSL library. This library always appends prefix to public key bytes (this is standard encoding defined somewhere)