[andrew]

The MOROP standards are a good guide for track and structure clearances, and are available on their website at http://www.morop.org/en/normes/index.html. NEM 102 and 112 are useful, though possibly a bit conservative. They cover H0 rather than 00, but presumably it should be safe to scale them up 14.3% to give a rough guide for 00. The track separation they give for H0 is 46 mm, which works out to 52.6 mm between centres for 00 straight track. There's other good stuff on that website too, such as NEMA coupling mount information.