20 Ga. double barrel choke size

I am looking to buy a Winchester Model 21 20 Ga. double barrel marked mod. and full. The barrels measure .06 and .18. Is this the correct choke size for this configuration. The owner says he thinks it may have been opened up some time ago. The price is good enough that I think I will buy it either way but I would like to know the correct choke. Thanks ahead of time for the help.

MONEY TALKS mine says good-bye