There is a guy selling a steel 120 round drum on gunbroker. looks like a modifyed AK.
Anyone know the scoop on these?

Quoted: There is a guy selling a steel 120 round drum on gunbroker. looks like a modifyed AK. Anyone know the scoop on these?

Youn mean this:
Link

Unless you are a collector, it would be more prudent to get a Beta C-Mag. New C-Mags can be ordered for about $ 240. That's just $ 45 more than the 120-round drum. I bought the drum years ago to try it out. It works but the spring winding mechansim is a bit finicky. The cons are:

a.  Too heavy (remember in the AR15 type mag well, the only thing holding the weight of the fully loaded magazine is the mag catch)

b.  Protrudes too much underneath the gun for effective prone shooting or bench rest shooting.

In the end, if you want a drum, the Beta C-Mag is the way to go. However, nothing really beats the overall reliability, durability, cost effectiveness and portability of your USGI 30-round magazine.

The Chinese AK drum mags are the best in AK drum mags. I'm not sure about modified Chinese AK drum mags for the AR15.