Back to mechanicals...
Since using my EQ3-2 mount for the Sun scan takes 3 minutes (when tracking is disabled), I searched for a quick solution for suitable tracker.. and found
this one (The first one, tracker).
The only variables I needed to modify were
TIM_FAST. and
char sm_tab[8][4] (I am using full step with pause to save power).
The rest was OK for my mechanical setup.
New electronics (Arduino NANO) will fit inside EQ3-2, inserted into existing PCB (designed for 68HC705KICS (pic attached), which I still intend to use for that mount).