Stick a temperature probe right at the carb and measure the difference between the setups. There are paper thin digital probes made for PC hardware setups (and cheap) that work great for tinkering with motors. You can slide them in between gaskets and torque the bolts right behind it with no damage.

I used one of these probes right at my upper plenum when building my cold air box for my efi 306cid build (pics in gallery). I tried a few different locations and snorkel shapes before I found one that snagged the coldest air. The colder the air, the denser, and more o2 rich.

Believe it or not, slight angle changes in air direction, deflection, or input location can make a big difference in charged air temperature (up to 25-40* difference). With a temp probe, there is no guess work. The probe and meter cost me $30 with a 12v dc converter.

RexB the power increase probably wasn't your imagination with the aftermarket filter element. I gather you found a way to feed it colder air, from a wider, and less restrictive area.

*note* Be careful with those teeny weeny thermostats... 160* and below do make performance gains at the cost of metal deterioration of your inner parts. If its more than a drag strip truck or trailer queen ... I'd run a 180*.

Just my $0.02 and keep those pictures coming! I love the old 70's F-bodies!

Keep on Truckin!
Mike