Here is a Parker DHE Reproduction 2 Barrel set in 28 GA. These guns were made in the late 80's and early 90's in Japan for Winchester. The parts are virtually interchangeable with the originals. They were built in 20 GA at first and then 28 GA. There were about 4000 28 GA sets built and slightly more in 20 GA. There are even a few sets with both 28 GA and 410 GA Barrels, that would be da bomb. There was a time when you coulda bought these new for $3000.00. That day is gone and these have become increasingly desirable especially in 28 GA. Today these 28 GA 2 Barrel sets trade in the 6K range, and going up quickly. Single barrel 28 GA in the 5K range. Single barrel 20 GA at 4K. That gives an order of things.
If you had a choice between the 20GA and 28 GA the push goes to the 28 GA. Simply because an original Parker in 28 GA DHE is going to cost you 35K to 40K with about 80 guns made in that GA. Whereas a 20 GA Parker will set you back around 20K, and is much more readily available in the market place. Sooner than later the 28 GA repos are going to be gone, all sucked up because of this fact.
As a side note there is an outfit that has 16 GA Barrels for the 20 GA repo, that would be a wise expenditure of money.
As another side note, Connecticut Valley Firearms..Gazalans is building a Parker A1 Special in 12 GA for Remington for $48,000.00 a copy. Not as a repo but as a continuation as Remington was the last owner of Parker.