I am curious how car bodies were made back in the 1950s. Specifically the micro-car bodies like the Isetta. What techniques and tools were used back then? They seem fairly simple. Could a body for an Isetta be built in a small shop?
I don't think there was anything special about the manufacturing. Pressed steel sheets for the panels which were welding together.
The biggest cost specific to the Isetta would have been the dies used to press the panels. The presses could have been used for any similar-sized panels. The original Italian manufacturers also produced motor scooters and refrigerators, not "full size" cars.
Some pictures of the UK Isetta assembly line here: http://www.isetta.org.uk/page16.html
The UK assembly line was constructed from scratch in just 3 weeks, in a factory space which had previously been used to repair railway engines. That suggests there was nothing particularly novel about the processes used.
For the Isetta you can see that the overall body shape is quite flat and boxy, without the more pronounced compound curves of other cars of the period. This makes it relatively easy to produce the panels.
As well as die formed pressings there are various manual methods for forming sheet metal body work using tools like power hammers, swage tools and english wheels. These are still used today for small volume and custom car bodies although they are highly skilled processes they are certainly within the scope of a small shop.
This is also the start of the period where you begin to see to see proper sports cars with specifically designed light weight space frame chassis and aluminium and, later, fibreglass body-shells, often using fairly standard engines and transmissions as opposed to the pre-war tradition of very basic ladder chassis with bigger and bigger engines.
Traditionally there was a distinct separation between the engineering aspects of the, engine, chassis and drive train of a car and the coachwork and interior of a car but the pre and post war period started to see this becoming more integrated.
There were a lot of small volume cars made in the 1950's as the post war economy in Europe meant that there was quite a lot of surplus material and industrial capacity but not much cash for investment in new tooling so it is common to see cars with relatively advanced design but with quite simple manufacturing processes, often making use of post-war surplus materials and parts.