a chain tensioner is not for so much for alignment but... tension. many older steel bikes have horizontal dropouts which will allow adjustment of the wheel for proper tension. Alignment depends on several things, the bottom bracket width and the rear wheel dish. Its pretty eash to redish the rear wheel and adjust the spacers.

The chainring can also be placed on either the inside of the crank or the outside. A friend just did a conversion and he had to use the smaller chainring as a spacer for the big chainring to align the chainline.

Chainline is critical with a fixe, good luck.