Actually it is 128 : 1 saving since the MEGA version defined step_count as a int where as the UNO version defines it as a uint8_t.

Thanks Krishna.
After a lot of tries, I managed to get the code to run on an Ardunio UNO. See https://www.hackster.io/john-bradnam/reducing-your-memory-usage-26ca05

Hi Thomas
I finally got around to making one :-)
My aim was to reduce the size of the final unit and make it no wider than the LED Matrix itself. The software has been modified to fit in a ATTiny85 and I have 3D printed a case for it. You can find my variant at https://www.thingiverse.com/thing:3877685