Hi Garry,
take a look at a relatively new firmware @Toykeeper has written.
It’s named “biscotti”.
Written for the 105D, offtime memory without cap by using brown out detection (BOD). And she crammed in all functionality the 13A with 1 kB can take.
You find it in Toykeepers firmware repository.
Just be sure to use the right fuses, there are reports of bad timing when flashed incorrectly.
EDIT: And take a look whether you already got the driver version where pin 5 of the attiny seems to be connected to ground. You might need to cut this for biscotti to work as intended.