Hey-Hey!!!,
The 6V6 is the closest of your choices. The 6K6 has a Loctal analog, but that's another socket and re-wiring job. Any particular reason to use something other than 6K6? They're not so expensive compared to your substitution options actually...
Check Duncan Amp's TDSL. The 'Tube Data' link at the top left of the page. Look at Frank Philipse's page, some of his stuff does not reliably show up on DuncanAmp's search.
http://home.wxs.nl/~frank.philipse/
( I can only Hot-link one at a time )
regards,
Douglas