If the housing gets overfilled the lube will seep out of the input shaft area and contaminate the clutch. If there's wear in the driveshaft bushing just behind the universal joint ball, the lube can seep down the torque tube and overfill the rear end, resulting in leakage at the rear axle bearings and brake contamination. Since the spinning gears in the trans splash lube all over inside the case, if you can touch the oil through the fill hole in the side there's plenty of lube in the case. A slightly low oil level is better than over full. Don't use fancy synthetic lubes in a stovebolt transmission- - - -plain old 90 weight mineral oil is all it needs.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!