Shelby 400
Whilst I may be little help Don Pilling in Queensland at Snake Bite has recently supplied my wiper assembly - two blade - he is currently supplying and also installing his own three blade units.
Sorry but my measurement for the two blade are at 440 centres, that is 220 in either direction from the centre. However this does not obviously give the coverage % you get from a 3 blade setup.
I am reluctant to say put one in the centre and then go 220 either way as there would be a heap of overlap.
No doubt you will get some response from the Thread but this will give you a starting point and perhaps the centre and 220 is correct.
Cheers
Bernie