What are the measurements of the stand? That would be easier to tell.
Although, looking at it I'd think a 55 is too tall or very close. You might not be able to actually get anything into the top of it because it may be so close.
Typical dimensions:
55 Gal: 48 1/4 x 12 3/4 x 21
75 Gal: 48 1/2 x 18 1/2 x 21 3/8
Even if it did fit,& the stand could hold it,I wouldnt do it.
I think the 55 would be difficult to service,& would sit to low to be viewed comfortably.
That doesnt look like a fish tank stand it looks as if there is already alot of stress on the bolts. it looks like 1/4 inch of wood holding what the tank is resting on. I would just pricematch a build your own double level stand and get the 55. 50 is better though much more boxy more room for turning. impo