Poland Groszy Provisional Issues 1950 - 1952

Is there a list of which Polish stamps were overprinted and handstamped with "Groszy" using Scott catalogue numbers?

There sure is. Wladislaw Kolakowski's "Groszy Overprints", self-published in 1952. This is THE English reference for these issues. Bits & pieces of new items have been sporadically discovered since then, but he has catalogued the vast majority. He's got some serious tables at the back, prices are out of date of course but a good guide to relative values.

A quick google & Amazon has one
http://www.amazon.com/Polish-stamps...p/B0007G15EM

But if this Subway price is correct, $2 is a steal, don't hesitate in buying it.
http://www.subwaystamp.com/POLAND-G...tinfo/RDD75/

Ben Nieborg's Polish stamp site has an excellent introduction to the Groszy overprints
http://www.groszy.pl/wprowadzenie.xhtml

But if you've got a couple of days free time, this is where to go. He's got everything. Complete. 100%. An amazing life-times work
http://www.groszy.pl/wprowadzenie.xhtml

YeaPolska - that's excellent reference! Thanks for sharing, no I can have another look at these.

The correct link for Ben Nieborg's Groszy information...

http://www.stampspoland.nl/

Oops, here's the direct link to Ben's Groszy page
http://www.stampspoland.nl/series/g...y_intro.html