I got this problem beat and figured I would post for anyone searching in the future. There were multiple problems with the old system....
The conventional style expansion tank wasn't installed using an air seperator. I am confident that I could have kept the conventional style expansion tank if I used the B&G IAS (Only the 1.5" and bigger versions have a 3/4" npt port on top, the smaller ones use a 1/8" npt port) and plumbed the top fitting to the expansion tank, keeping the pipe from the IAS to the tank uphill at all times. In fact, this was my original plan, and was going smoothly until I realized that this was **impossible** with my current setup. The main pipe in my system is very high. By the time I plumbed in the IAS to this line, I would have had to run the pipe from the IAS to the conventional tank downhill...not going to work properly. Automatic bleeders should not be used with a conventional expansion tank, as all the air in the system should be directed back into the expansion tank.
The second problem, for me anyway, was the location of my circulator pump. I was simply copying the install of the oil boiler when I installed the circulator on the return side of the boiler. My circuit was as follows:
circulator -> boiler -> conventional expansion tank -> check valve -> baseboard loops -> pressure regulator/make up valve -> circulator
After extensive reading, much of it on this site, I decided to pump away from the expansion tank. This was an easy decision for me, as I was moving the location of the expansion tank anyway and installing an inline air separator. My current circuit is as follows:
boiler -> check valve -> air seperator with auto air vent on top, and diaphragm tank on bottom -> circulator -> baseboard loop -> pressure regulator/make up valve -> boiler
I got the new parts installed and replaced the old circulator location with a piece of copper, let water into the system, and had 2 small leaks. I drained the system again and took care of the leaks then started filling the system again. I was running the circulator and purging the lines via hose bibs until the hose stopped spitting and sputtering. Then I shut the hose bibs down and let the air seperator do its job. Less than 24 hours later I have no more gurgling noises, no more hissing from the automatic air vents, and feel much more comfortable with my setup. All in all it took me about 10 hours to do this whole job, and that included 2 trips to the hardware store at 45-60 minutes each, and trying to thaw out a frozen garden hose until I borrowed one from my neighbor.
Here is a pic of the results: