Predecessors

B20 on the left, special-bodied Aprilia on the right.

Where did the B20's lovely body design come from? Too often we look for the master stroke, the sign of genius, the heroic inspired moment as the way great design comes into the world. But looking at the B20 (and a number of other cars from the same period) stymies this approach: its not just the product of Lancia and Pininfarina, there is even doubt as to who's hand was behind it.
There is another way to look at this - not to consider the design as a singular spark of genius, but rather as a product developed in a context, as one among many. The time was full of designers working to figure out the post-war coupe, sharing their ideas among other designers as carrozzeria prepared special project cars for  the major automobile shows held each year in Paris, Geneva, and Turin. Their goal was to attract both customers and manufacturers, by continuously pushing design ideas forward. In Italy, special bodies were found on Ferraris, Maseratis, but also they were prepared for  Lancias, Fiats and Alfa Romeos.
Looking at the work years later, we can see this was a time when designers looked, learned, and shared from each other - as part of a tight community working on the same products but with slightly different answers. In this way  antecedents for the B20 are not just in the Cisitalia 202, but also in their Aprilia coupes ( late 1940s to 1950), and in Ghia's Fiat 1400 Supergioiello, possibly by Michelotti. 

1950 Aprilia Speciale by Pinin Farina

The Fiat 1400 Supergioiello by Ghia: 

Or the same 1950 Ghia Fiat at the Torino Auto show (thanks to Paolo Giusti). It has very nice lines, similar but exactly not same as the B20.... 

Supergioiello at the Torino Salon dell'Esposizione in 1950