With an old engine chances may be that either the bores and/or piston rings might be a tad worn causing an increase in pressure within the crankcase, which is in no way unusual, perhaps even less so for a rarely used vehicle..? In times past the norm was to just vent the crankcase to atmosphere. As Dave suggested in time the vent was redirected into the air filter housing, in order that the vented fumes would burn in the combustion chambers..A worn engine would generally foul up the air filter with oil mist at the point where the vent tube entered the air box...
From a very dull memory early TR`s may have had a wire mesh filter built into the oil filler cap on the rocker cover, which if full of crud could be washed out in a bath of paraffin or similar.
If your engine might be a tad worn and uses a little oil in your usual/expected mileage, then perhaps a breather could be directed to an aftermarket oil catch can to keep the engine a bit cleaner...?
