I am having trouble getting a crankset to fit on a Shimano UN55 BB Square Taper Bottom Bracket (68x127.5mm).

Neither a Shinano Alivio nor a Vuelta Pista crankset seem to correctly sync with the square taper bb. There is a gap - I've mounted both and posted the photos below.

I've been converting an old 70's Nishiki to a fixed gear and updating the parts. I feel ignorant and don't know what question to ask to find the part that will fit. Any help is greatly appreciated.