I fitted one of these to my Maserati in Australia.
http://www.carbuildersolutions.com/uk/aluminium-washer-tank-vertical

They also do a horizontal version.

http://www.carbuildersolutions.com/uk/aluminium-washer-tank-horizontal

It may be necessary to drill a tiny air hole in the top of the cap if it forms a vacuum and can't pump water to the washers.

On the Maserati I made the hole a little too large and water came out of the bottle some how when the car was under way. I resolved the problem by finding a suitable inner plastic cap, such as you find under the cap of some oil bottles, and I put a small hole in that.

I think the aluminium is more suited to the Morgan.

Peter

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