Keep say eight thousand building blocks in the OXO Tower? (10)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

STOCK (keep) CUBES (Building blocks) OXO is a brand name for Stock Cubes, but I cannot explain away “eight thousand” (20 cubed?) in the clue. The OXO Tower is now an art gallery on the South Bank of the Thames between National Theatre and Blackfriars Bridge. From Comment #2: Eight (8 = 2^3) and thousand (1000 = 10^3) are both examples of cubes (thus the final “?”) I might have not read 8000  and treated them separately if the clue had been worded “a thousand and eight”