Consider my low tech option.
Place a black film leader etc in the negative carrier, emulson side up. With a pin, scratch the emulsion off around the edge of the carrier, ensuring that film is held firmly in place while doing so. Take the film out of the carrier and use a steel ruler, scribe in diagonals across from corners of the rectangle or square that you scribed. sweep off the emulsion burs.
Put this test neg the regualr way, emuson down, in the neg carrier, and project it.
Check for sharpness of image, measure the length of the sides, etc to check for things all being the same length, etc.