William -- if you have a complete 356 donor looking for a project, you might find a better home for it with a speedster shell rather than a spyder. The spyder is an entirely different car (tube frame vs. pan chassis 356, mid engined vs. rear engined 356, etc.).
The issue with the 356 drum brakes that initiated this thread comes from the deal that all spyder replicas are built with VW ball joint front suspensions. Earlier VW "link pin" front suspensions would be directly compatible with the 356 drums. So, in essence, an off-the-shelf new VW link-pin torsion beam assembly would do the job for a fraction of the cost of an authentic vintage 356 version of the same thing. In the 356 and VW, the torsion beam is a bolt-on component so conversion might seem relatively easy. In the spyder, however, the beam is a welded component of the tube frame -- so what you got is what you get.
If building from scratch, a link-pin torsion beam could be used when the frame is jigged. But few customers would want a link-pin torsion beam -- unless going to the big pu-bah cha-ching of 356 drums is the intent.