scotty,
both pedals may move when the clutch is pressed but it is the linkage between the two that makes it appear that way. I believe the design is made so when the brake pedal is pressed it disengages the clutch at the same time, so naturally when the clutch pedal is pressed the brake pedal may move down a little.
As for the oil used, it sounds like it has an oil clutch so yes the transmission fluid would be the same as the clutch housing fluid.
Some units did circulate the hydraulic fluid into the differential but i would check the differential tubes for a dipstick or a dipstick pointing out from the front just under the right side of the firewall/kickpanel between the mast and firewall panel. If you do not find one there check for a level plug in the differential housing bell in the front.
As for the engine, i never saw an IH engine in one of those but i know they did use a chrysler slant 6 in some of their units, probably the G51 series. I didnt run across too many L82's in my area.