Holes w/ plugs in airbox! ???

[undysworld]

This afternoon I was asked to help a local owner with a 710K which was acting like it "ran out of gas". (Turned out to be leaking fuel lines, which apparently sucked in air.)

While removing the airbox to prime the carbs I noticed that there were two holes, maybe an inch dia., more or less directly above each carb, with rubber/plastic plugs. I'd never seen these on a truck before, but my assumption is that they are there to allow priming the carbs w/o having to remove the airbox, etc. I didn't remove the plugs, since the airbox was already off and since they appeared rather brittle.

Can anyone shed some light? Thanks.