G'day folks,
Interesting older machine you have there, Lorenz.
As CyberJack has said, that blade plate setup has been cobbled up by a 'previous tenant'.
The Whirlwind slashers all used sickle bar hay mower 'knife segments' for cutting blades AFAIK; the later models went to a triangular blade plate, with three knife segments bolted to the vertices - as mentioned in those ads Jack has posted.
My family's OPE business was a Whirlwind dealership in the 1970's, up until they were bought out by Masport NZ in around 1975. We used to get a few of these older slashers in for repair; they were a very durable and well built machine.