I guess it was more the overall look of it that appealed, the classic long transom, broad stern and fine bow, I didn't discern too much shape distortion from that photo but I'm not too familiar with Nissen designs.
The discussion by sean9c re the propellor/engine issues with Timschal are interesting. With some of the bigger heavier boats there were some efforts to get a shaft drive extension (or something like that) down into the keel to maximise the prop depth for the EPF measurement. As best I can figure the rule did seem to even out the relative costs and benefits of various prop and shaft installations but there was probably a lot of optimisation going on in this area as much as any other.
I think too that there were often a few hasty engine modifications at various regattas while crews tried to get their motors to achieve a speed under power equivalent to the square of the L measurement (or thereabouts? - PaulB?). Certainly Candu II came close to not qualifying for the Half Ton Cup in Trieste with an outboard that took a bit of tuning, they passed the test in the end by just .2kn.
Also interesting that in '76 MB had a giant outboard, they really had to wrestle it out of the boat. The thing flew under power
