£69 for a simple back plate seems a little OTT…Unless I’m missing something
main difficulty is getting nose dimensions correct:

There was an article in MEW (No 102 Nov 2004) about making it, using fitting gauge.
There is also an excellent YT video about making short taper dial indicator/gauge to help with making it
(if you have original good quality master backplate to compare):
I have produced (successfully) backplate of this type for my lathe,
which has DIN 55021 spindle (same as D1-3).
It can be done, but to be honest… considering what’s involved in getting it right,
next time I might spend £70 with Warco