Michael,
The 59 certainly had the biggest boiler (7'6" dia) and the largest wheels, the 20th was slightly smaller (3" less on both boiler and drivers) but these are two of the three best looking designs built, the other one is the NSWGR AD60 4-8-4+4-8-4. All had the chamfered front tank. My absolute favourite is the the Rhodesian 15/15A 4-6-4+4-6-4.
The dimensions section of my website took a long time to compile, especially as I had to convert a lot of dimensions to imperial and recalculate all the TE's to the same % bp.