If you use Conference pears instead of Nashi, the macros for each muffin will bear no significant difference. As they're sweeter, I recommend that you REDUCE icing 'sugar to 1 TBSP and OMIT pure stevia powder when mixing dry ingredients.
Stir the chopped pears constantly to begin with, otherwise the cinnamon/icing may stick and burn; after a minute or so, the pears will start to release their juice, so you can stir less often.
I use Sainsbury's Smooth 100% Almond Butter, which has a superior flavour and only contains 4.3g net carbs per 100g. Different brands may well contain more carbs.
The only way to ensure accurate measurement of ingredients is with Metric Kitchen Scales. Click
HERE for the ones I use, or
HERE for U.S. alternative.