I have been looking at this a bit. The standard wiper blade is 175 mm long but the centre pivot is not at the centre, it is 80 mm from the end closest to the drive spindle (7.5 mm off centre). Seems strange but I have seen that some other car blades are not symmetrical but this is a lot for such a short blade. The little metal parts on the "manufactured" blades have the centre pivot 5 mm off centre too.

With the "manufactured" wiper blades it is possible to adjust the effective position of the centre pivot. The short end can be set so that the wiper, at the end of its stroke,does not come over the lower screen frame. On measuring I discover that there is 15 mm difference between the lengths of the inner ends.
Driver's side = 75 mm
Centre = 65 mm
Passenger's side = 70 mm

What this means is that even in the best case the end of the standard wiper blade is going to hit the frame, thereby shortening the life of the blade.

This difference is because of the curve of the lower frame. Naturally I can't guarantee that all Morgans, left and right hand drive, have the spindles in the same place.

The length of the wiper arm from the centre of the spindle to the fixing "dot" of the bayonet is about 175 mm (the same length as the blade). With the current standard blade it would be better if it was 5 mm longer for the driver's side blade (any longer and the blade would risk hitting the side frame) and 15 mm longer for the centre wiper. Clearly an adjustable arm would give the possibility of 3 different lengths. If I could find a wiper arm with a fixed length of 190 mm I would be reasonably happy with that.

Regarding the headlight wiper blades I have been unable to find any that are 7" or 175 mm long. It would be no problem to get one slightly longer and cut down the rubber and the spring steel as the way they are made seems almost identical to the home made version.

Naturally we are still left wondering why MMC have not come up with a better solution as the numbers involved would easily warrant having a longer wiper arm (would not cost anything)and decent blades which might cost a few pence more.

Peter

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