So how DID Lionel assemble those E units?

They are tricky but you do get better the more you do.  I wish there was a big secret but you do need 3 hands at least.  I try to work from the top down when reassembling and hold the 'ears' as I get the individual pieces in place.  First, the 4 finger, then the drum then the two fingers.  It still takes me awhile though and usually quite a few attempts.  

I just did one last week. The nub went bad on the end of the drum and the fingers shorted out.

How do the guys who repair clocks hold everything in alignment while they reassemble the works?

I believe Lionel had a special vise to help hold the unit. The number for this vice was ST378. Lionel also had a special tool to help spread the unit. Once the e-unit was popped open the fingers and drum fell out.

Not sure if it's still available, but a few years (at the suggestion of someone here on the forum) I found a video on YouTube on repairing/rehabbing E-units. It was in two parts and was excellent in terms of the video quality and the instructional end. Highly recommended if you can still find it.

Don't forget that the other end of the e-unit pry tool has a hook on it. It's used to grab the drum and put it/hold it in position. 

Roger

I used a screwdriver held with 2 fingers for drum maneuvering and holding one finger panel in place, and held other finger panels in alignment with other 3 while pressing together frame with 2nd hand.

This maybe the video on YouTube showing how to repair a Lionel e-unit.

This is the E unit vice that came with my press...I never had occasion to use it.

I believe Lionel had a special vise to help hold the unit. The number for this vice was ST378. Lionel also had a special tool to help spread the unit. Once the e-unit was popped open the fingers and drum fell out.

I have the ST-378 e-unit vise. I find that it is easier to just hold the e-unit in my hand, so I don't use it.

The vise that Bob Taylor shows is the modern equivalent. It is made by Hobby Horse. They were offered for separate sale by Hobby Horse. It was included in the Lionel Service Station tool package from the early 1990's. They are still available.

Hennings also has a more elaborate vise / jig for assembling e-units. I have one, never tried it.

I do use the e-unit spreader bar. I think it works well. Replicas are inexpensive.

I've had a lot of practice rebuilding e-units

Thank you everyone for your replies.  This was a once in life time repair deal for a friend whose dad had given him the train.  Engine was dead shorted and I found that the lamp lead had gotten pinched and rubbed through,and the E unit barrel was broken.  The wire was easy, the E unit was a challenge.  But I did it abeit, adding few more white hairs.

I saw that hook but had no information as how to use it for E units.  But unit is assembled and working.

Another tip: The thickness of the e-unit spreader bar is the same as the spacing should be between the e-unit contact fingers.

Here are the Lionel Service manual pages on postwar E-units.
These pages make no mention of the tools because the pages predate the tools.
I thought there was documentation on how to use the e-unit spreader, but I don't see them on the Olsen's site.

A lot of good information here and some very fine tips.

Never used the vise just the spreader bar. Almost 50 years of doing them I can do one in my sleep. Practice! :-)

I'm thinking of buying a pair of lock ring pliers for spreading E units.  Anyone have a recommendation on which one I should get ?

@mlaughlinnyc, I like the Craftsman 4735 I have for my trains.