The 3.5 E3 is sort of a hybrid between a 3.5 E, a 3.5 F type 2 and a 3.5
F type 3.

1) The 3.5 E3 has the EVS meter system of the E, hence there is no
filter compensation dial on the focus knob side. Also the 3.5 E3 takes a
"T" type meter, not an "F" type meter.

2) The 3.5 E3 has the peep window like the 3.5 F type 2, where the
apertures are closer to the body and the speeds are closer the front of
the camera.

3) The 3.5 E3 has the front plate of the 3.5 F type 3. ie: below the
taking lens it says "Made in Germany" on top of "Franke & Heidicke".
This is reversed on the 3.5 F type 2. The self timer on the E3 is like
the one on the 3.5 F type 3. There is a difference between the self
timer placement between the 3.5 F type 2 and the 3.5 F type 3.

4) On a 3.5 E3 the handy exposure table on the back of the camera looks
like the one on an E type camera as opposed to the ones found on the F
type cameras.

> There is one more similarity/difference that I neglected to mention that is
> rather important and that is the 3.5 E3 has a 45 mm interlens distance
> (between the centres of the taking and viewing lenses). The 3.5 E (serial
> numbers 1,740,000-1,870,000), and 3.5 E2 have a 42 mm interlens distance.
> This makes a difference for accessories that take advantage of both
lenses at
> the same time, such as the Mutars and lens caps. A 3.5 E or 3.5 E2 lens cap
> will not fit a 3.5 E3 or 3.5 F camera and vice versa. 


here links to a nice collection of images made from Rolleiflex 3.5E3