Can anyone say what reach the SunTour Vx rear dérailleur has.

I have 42/52 in front and (6-speed) 12, 13, 16, 21, 26, 31 on the freewheel.
Now donīt suggest me to try it to know if it might work. I do not have all parts to run a practical test. Otherwise it would be the obvious solution

I also wonder if I can take for granted that a freewheel marked with "REGINA CORSA 2 ITALY 78" has italian threads? Is it made in '78 and therefore the number "78"?

Thanks for any input in these matters.