As Louie said, E stands for the compressor cover (aluminum cover that has the air inlet and discharge) To my knowledge, there is no such thing as a .62 A/R turbine housing (cast iron exhaust side). There are only .63 and .85 Precision Turbine housings and some who will machine a Garrett .63 or .82 A/R turbine housing to fit the T350 turbine wheel. Another misconception with turbos, is that both the compressor cover and the turbine housing both have an A/R number. The TO4E compressor cover (3" inlet, 2" discharge) that PTE makes has an .60 A/R, and the TO4S compressor cover (4" inlet, 2.5" discharge) has a .70 A/R. The A/R numbers on the compressor cover does not play as large a roll as the A/R number on the turbine housing does. The A/R number on the turbine housing directly affects spool up time, torque converter requirements and your horsepower curve. Ex: a .63 A/R turbine housing will spool up quicker and make more hp and torque at a lower rpm range than a .85 A/R turbine housing will. But in some instances you can push a .63 to the point that back pressure starts to get out of control. (Ex: People trying to push a P-trim turbine wheel equipped turbo with a .63 A/R housing too far on a combination, such as a TSM combo, that would benefit from having a GT-Q turbine wheel equipped turbo and a .85 A/R housing.) This is why you see 95% of the turbos on the market for street driven Buicks having the .63 A/R. The .85 A/R is typically for serious combos (575 and up) that are trying to make the most hp that the turbo can support, as well as freeing up the exhaust on a seriously built motor.
HTH
Patrick