TomD
3 thoughts on the mouth:

1) Does it look like it was jackassed around with by someone who didn't know what they were doing? Or used by a pro to earn a living for a lifetime?

2) Based on the pitch, performance, does it seem like it was designed for what you do. For instance you only work ebony, but this was clearly set up to joint barn boards.

3) How is it working for you? If it works great, the wider the mouth the better. A wide mouth is better when a plane otherwise does what you want.

PS Look and see if the mouth, and plane sole are flat, that can also affect the quality of cut.