Slant 1 barrel air cleaners
That's not a singular answer. There were four physically different air cleaners commonly factory-installed on Slant-6s between 1960 and 1963 (actually thru '69), even if we look only at passenger cars and not trucks or vans. If we drop that "commonly" filter, the total runs to around six or so.
A more detailed question is needed. What car is this for? Some of the air cleaners on the list don't fit some cars (okeh with a 170, no hood clearance with a 225 on some cars). What're you trying to learn/do/fabricate? A twin-1bbl setup, maybe? Something else?