Glad to hear it's working out for you.
As per Peter's comment, sharpness of the 60-250 is such that you can crop, crop and crop some more
I bought the HD 1.4x rear converter for use with the 60-250, and I do use it from time-to-time, but often I'm lazy and just crop. The K-3 / K-3II's sensor and the sharpness of the lens mean you can be quite aggressive and still get very detailed shots.
As an aside... Though it's not the lightest bit of kit to hand-hold for long periods, it makes a fine portrait lens too. I've only played around with it in this application, but I really like the results and intend to do some planned portrait shots with it. At f/4 it's not going to offer really shallow depth-of-field, but with a reasonable distance from subject to background, the bokeh is lovely