Railcraft's boilers are awesome, but sometimes you can't get the right sized boiler you need. So this mod lets you add custom sizes to Railcraft's boilers.
This has been tested with Railcraft 22.214.171.124 but it should work with older versions. Custom sizes are set via the mod's config file. By default, 1x2x1, 1x3x1, 1x4x1 and 2x4x2 are added as custom sizes.
The source code for this can be found on my GitHub account.