Without clear markings, I'm only basing my answers by looking at the style of the unit -- it does have a standard single stage, two piston pump. Maybe 1970's vintage Speedaire (or Sears) 20 Gal. model (both were usually green in color and Speedaire did supply Sears for years). The motor should tell you the HP rating. If it's 2-3HP, and 220volt, then it's rated for about 7.0 CFM at 40psi and 6.0 CFM at 90psi. Sears also sold a 4HP 20 Gal. model in those days that was rated around 8.2 CFM at 40psi and 7.0 CFM at 90psi.
Actually, I looked at the pic one more time, and it looks like a stationary unit that soemone converted for mobile use (notice the home made risers on the front legs). If it's a stationary unit, it will likely be a 28 or 30 gallon tank.
Not much of a performance improvement over your current 33 gal unit; except that it's a lot quieter and definitely better quality
It's worth about $75.00, assuming everything is working and in decent shape -- especially the condition of the tank.