I have an Omega D5XL. It's wall-mounted and cross-braced with a set of DIY custom heavy-duty threaded rods and individually adjustable turnbuckles. Using these turnbuckles I can control front-to-back tilt of the overall unit and rotation around the vertical axis at the base mounting plate to a coarse degree. But for fine adjustments you must use the controls mentioned by Mike.
I ran across this Omega D5 alignment page on the Zig-Align website that might be worth posting for future APUG search references.
It describes a brief procedure for aligning the lens stage of this enlarger using both the eccentric rods and set screws (front-to-back tilt) and the adjustable brake track (side-to-side position). First the lens stage is adjusted. Then the negative stage is independently adjusted using its side-mount bolts. A diagram is included.
According to the above guide, alignment of an Omega D2 "is not the same in detail, but it is similar in general."