How to use ABC Extended with standard British PC keyboard layout

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The ABC Extended input is fantastic for inputing several diacritics, but it only seems to assume apple's own layouts, i.e. it doesn't recognise the standard British PC layout. Is there a way to make it work with the standard British PC layout, particularly re: the symbol mismatches between the two?

Standard British PC has shift+2=" and shift+'=@.

The Apple British layout has shift+2=@ and shift+'=".

In British PC, the key left of 1 is ` ¬, but in Apple British it is § ±.

In British PC, the key left of z is \ |, but in Apple British it is ` ~.

In British PC, the rightmost key of the asdf row is # ~, but in Apple British it is \ |.

Suppose I definitely do not plan to use the Apple British layout at all, but may need to work with the standard British PC layout. Is there a way to reconfigure certain things for the ABC Extended input to be compatible with the standard British PC layout?

Best Answer

Update -- Problem solved with Ukelele. I copied the layout of the current input source and then manually adjusted the key mappings (including the shift modifications etc.). It took me just a few minutes.