Thanks for all the suggestions.
I am finishing a partially completed loco so all the existing fasteners are BA, a change to metric is not possible.
As for turning down the large washers, this is possible, unfortunately the large washers are about 3 times thicker than the ones I used to buy.
Many of the screws and bolts are visible so the thinner, smaller washers would be perfect.
My guess is that suppliers are substituting the M3 washers for the older 5BA washers due to availability.
Thanks
Keith Wood