I'm not arguing in the least. Remember I'm the one who came here asking advice, but these are quotes from the Browning website. However it is an article on backboring and I may have things out of context. At any rate I've checked the barrel and it is indeed an Invector Plus. I don't have the tools required to measure the internal barrel to know for sure if its backbored. But the initial question was simply what kind of chokes I needed and you've helped me find the answer to that.
............................................................The saga continues..........
"The Invector system is available for 12 and 20 bore Browning shotguns. The Invector system has evolved into two different versions : the standard Invector and the Invector-Plus for back-bored barrels. Depending on your requirements, there is an Invector system which will give you that vital advantage, whether hunting or target shooting."
"Invector-Plus System
These tubes have been designed for the new {{back-bored}} bands. A forcing cone which is too short and deforms shot can adversely affect patterns. This is why Invector-plus tubes have been lengthened and given a special tapered design. This ensures tighter patterns and more uniform densities. The Invector-Plus is only available for {{back-bored}} barrels. It is only suitable for 12 bore guns and is not interchangeable with the Standard Invector choke."
Thank you,
Broadbill