I really did not understand this question.
The enlarger base DOES NOT needs to be level. It maybe slanted to whatever direction you prefer. horizontal, however, is more common.
What you have to do is to align the HEAD so it's parallel to the BASE.
Transcribing from another site:
"Get 2 pieces of mirror, each about 4 by 8 inches. Leave one alone. On the other, take a razor & carefully scrape a small circle, about the diameter of a pencil, down to bare glass at one end of the mirror, about 2 inches in on the narrow end.
When scraped & cleaned, take this mirror and insert it into the negative stage of the enarger, with the mirror surface facing down, and with the clear glass "hole" end protruding from one side or the other. Place the other mirror, facing up, on the enarger base.
Now take your eye and peering through the small hole, orient the bottom mirror till you can clearly see the small scraped hole reflected back at you off of the mirror lying on the negative stage.
ANY misalignment will show up as a long trail of reflected "holes" going off into infinity. This rig is way more accurate than any level & easier to use.
For the lens stage, simply push the upper mirror up against the lens (it will not touch the glass) & repeat the experiment."