I’m thinking of the TT single speed project and I’m trying to think of some bikes that have horizontal dropouts. The problem with most track bikes is that they don’t have brake mounts or water bottle mounts and I need both. Of course we have the cervelo’s but what else? Both older and new models.
If you’re going single speed, not fixed, you can buy a Surly device (singleator?) to take up the slack and use a bike with vertical dropouts. You could also use an eccentric rear hub. There is a White Industries eccentric hub and possibly others.
If you’re not running a fixed gear, you can skip the horizontal dropouts all together and just use a regular cassette hub with a single cog and a whack of spacers on either side of it, and keep the rear derailleur to take up the chain slack. If you plan on fixed, remember most fixed hubs have a 120mm spacing, while most non-fixed dedicated frames have 130mm spacing. So you’ll need to get some washers and fill in the space between the hub and dropouts.