what you found under your airbox is the stock airbox feed. It too is very small and restrictive.
The tube coming out of it is the preheater hose connected to the pass side exhaust manifold.
To really benefit from the KKM you should provide it with a cold air feed.
What I did was cut a 4" dia hole in my firewall, where the stock feed used to connect, just below the battery tray on a 88 BII. Then I connected a 4" piece of heavy duty dryer hose and ran it up to the cone filter.
This flows nice cold air directly to the cone filter, sort of a ram air setup.
The next step would be to build a shroud around the filter blocking it off completely from any under hood air, similar to a full K&N FIPK kit.
You can also decrease the tempatures under your hood by running a 180 thermostat, using the larger 4 core aluminum radiator, supercooling fan, heat shielding, etc...
NO I already had my headers installed when I did the Granatelli MAS, it was the only mod I did at the time of installation. The Granatelli made a big difference in overall power and feel. The engine revs quicker and respondes faster tot he gas pedal. Overall power was increased, the largest increase was in the high end, above 3000 RPMS.
I WOULD RECCOMEND a larger MAF to anybody looking for more power from their OHV.
However, like always you are only as good as your smallest bottleneck. So a 70mm MAS will improve throttle response on a stock OHV with an airbox, but it will improve everything when you use it in conjunction with a ram air setup, intake tube, throttle body, headers and exhaust.
then of course ported intakes, etc.. go even further beyond that.
