Planning on getting a bike (Cadillac L-3) that only comes with a Nexus Inter-3/roller brake. Would like to upgrade to a 7 or 8 speed internal hub. Haven't seen the bike yet to measure, but I fear that the frame might not be the requisite ?130mm? , and it's an aluminum frame, hence no cold setting. Assuming the frame is wide enough, is this possible? If not, what are my options? 7 sp derailleur?

Thanks,
Marty

If the bike has an internallly geared hub it most likely does not have a derailleur hanger on the frame, so that would not be an option. If the frame is spaced right, you would just have to get the new 7speed hub and have a wheels built up around it. Any bike shop sould be able to take care of that for you.

My '68 Hercules with S-A 3-speed is about 125mm between the dropouts. That's narrower than the 7 and 8-speed Nexus hubs.

Doesn't look like it's going to work to me. I just looked them up in my QBP catalogue. It says the 3-speed Nexus is 120mm over locknut and the 7-speed is either 127 or 130.

If you don't have the bike yet, why don't you just look around for one that's equipped the way you want?

Your options are limited with this bike. Not only is the dropout spacing too narrow to accomodate a 7 or 8 speed hub(of any make), but it has rear facing dropouts making use of a derailleur difficult or impossible even with an adaptor bracket. Futhermore, only an older road type derailleur hub would be narrow enough to fit.
On to the next problem which is brakes. This frame has no bosses for cantis or V brakes, so your only option there would be a side pull caliper. Not impossible to do, but not a great option.
All in all, if you need more gears and you really want a pedal forward bike, I think the Townie 8 would be a better choice for you.
By the way, this is not a sales pitch as I sell Cadillac but not Electra.(See my response to your other post in the General Discussion Forum.)
Dan Burkhart
www.boomerbicycle.ca

Sturmey Archer/Sun Race 8 speed hubs are very narrow. They'll fit between drops designed for any other S-A hub.

Nope. sorry, that is incorrect. I have bikes with S-A 8 speed with drum brakes, and they are almost exactly the same width as a Nexus 8 with roller brake (About 132mm).According to Sturmey Archer's web site, the model with no brake is 124mm.
Dan Burkhart
www.boomerbicycle.ca

I'm not sure what model you have but according to Sheldon Brown the X-RF8 will fit as narrow as 118mm drops:

https://sheldonbrown.com/harris/sturmey-archer-hubs.html

Well, I certainly would not presume to argue with Sheldon on this, and I suppose it would be reasonable to use thinner lock nuts, but even so, I am pretty sure only the brakeless version could be narrowed down to 120mm.
Dan

This summer I saw a rod-braked Raleigh that had a 7-speed Shimano hub in it. He installed it when the original hub failed and said it made the bike WAY more rideable. And it didn't look horribly out of place. Of course I expect there will be some people spitting on him at the All British show this weekend...

If the Raleigh was a steel frame (and at that vintage, it couldn't be anything else) it could have been cold set to take the wider hub. The OP's Al frams can't be.