Hi Hans...I'm not sure exactly how much longer the 'long' dynamo is but if you are trying to identify one the body has two of the large countersunk screws that hold the field coil into the body...The short dynamo has only one for the shorter field coil..
I'd guess it must be about 1 1/4" longer than the short dynamo....Ian
The length of the main body excluding the ends (bearing carriers)
is
4 11/32" for the long type (E3LM-LO)
and
3 19/32" for the short type.(E3HM-LO)
Keith