Ok, shane, here's the scoop. Mike Orlen installs the truchoke threading in the Browning bps barrels for $55.00 labor. No choke tubes are included, but he sells them. Return shipping and insurance is $20. So for half the cost of your $150 barrel, you could have your current fixed full choke bps barrel coverted to truchoke tubes. Take the $75 you saved and buy some choke tubes. You'll love the versatility of being able to use a cylinder or skeet choke tube now and then for grouse or similar close flushing game situations.
With regards to the interchangeability between bps barrels, as far as I know, there are basically 3 styles: the long barrel tang extension (old style), the short barrel tang extension (fits on 2 3/4 and 3 inch magnum receivers), and the short barrel tang extension 3 1/2 inch chamber with the double step at the front of the rib (when viewed down near the chamber end) which only fits the 3 1/2 inch receiver. First, determine which barrel you have, it will most likely be the most common one, the short barrel tang that fits the 3 inch receiver. There are tons of them listed on EBAY each year. Very common. The other two versions still show up regularly as well. Hope this helps in your decision.
Update: I just pulled off my 20ga bps barrel. Short barrel tangs are approximately 1 1/2 inches on both the 20 and 12 gauge barrels. The long barrel tangs are around 3 1/2 inches long. Very easy to tell them (long and short barrel tangs) apart in a picture.
Also, buying a fixed modified bps barrel won't gain you much over your current fixed full choke. You will want interchangeable choke tubes.