I do not want to be overly pedantic in answering your question, but it isn't really a question of what I recommend, because the periods are an integral part of the indicator. Some indicators allow variation of the parameters to suit the trading time frame of the user. However, the Coppock indicator is a highly specific indicator, as described in my article in Shares magazine December 1999 (you can access it on my members' web site, or your local library (I am not permitted to give you a copy of the magazine article, because it is covered by copyright).
That quibble aside, the correct periods are 14, 11 and 10.
If you download one of my spreadsheets from the Resources/Data and Other Files page of my free web site, along the top you will find the calculations in detail. I set the spreadsheet up this way so that the whole thing could be maintained by hand and it would help people to understand the calculations behind the indicator.
There is also a MetaStock formula in Newsletter No 1 on the Resources/Free Newsletter Archive page of mywebsite.