A B767-300 CARGO FO DSNDS BELOW THE GS DURING A VISUAL APCH TO RWY 29 AT OAK; CA.

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DURING THE ARR PHASE OF MY FLT FROM ONT TO OAK; WE WERE CLRED TO ALVAR -- THE IAF FOR THE ILS RWY 29 APCH INTO OAK. THIS WAS FOLLOWED BY A DSCNT TO 10000 FT THEN 8000 FT. WE SWITCHED FROM CTR TO OAK APCH AND WERE ASKED (VERY EARLY) IF WE HAD THE ARPT INSIGHT. I DON'T RECALL THE CAPT'S RESPONSE (PNF); BUT WE WERE SUBSEQUENTLY CLRED TO CROSS 6 DME OAKLAND AT OR ABOVE 2000 FT AND APPARENTLY WE WERE CLRED FOR THE VISUAL TO RWY 29. I RECALL THE PHRASEOLOGY SEEMED A LITTLE NONSTANDARD. THE 2000 FT RESTR WOULD LEAVE ME ABOUT 500 FT ABOVE GS (APPROX 5 DME FROM THRESHOLD). I OPTED TO DSND EARLY; CONFIGURE FOR LNDG; THEN COMMENCE MY DSCNT TO THE RWY AT THE OAK 6 DME POINT. APCHING 4000 FT; THE CAPT REQUESTED I LEVEL OFF AND RECAPTURE THE GLIDE PATH. I DID SO; REMAINING IN LOC MODE AND STAYING AT OR ABOVE THE GS FOR THE REMAINDER OF THE VISUAL APCH. IN OUR DEBRIEF; FOLLOWING THE FLT; THE CAPT EXPLAINED THAT THE LEVELOFF HAD BEEN DUE TO HIS CONCERN ABOUT DSNDING BELOW THE FLOOR OF SAN FRANCISCO'S CLASS B AIRSPACE. HIS ACTION WAS THE CORRECTIVE ACTION. WE WERE NOT MONITORING THE SFO DME SO NEITHER OF US WAS CERTAIN IF WE DID IN FACT DSND BELOW THE FLOOR. CONTRIBUTING FACTORS WHICH LED TO THIS POTENTIAL VIOLATION; WERE THE OAK APCH CTLR'S DESIRE TO TURN US OVER TO TWR ON A VISUAL (OUTSIDE 25 DME) AND THE USE OF AN UNUSUAL RESTR AND NONSTANDARD PHRASEOLOGY. THIS; COUPLED WITH MY LACK OF FAMILIARITY WITH THE SAN FRANCISCO AIRSPACE AND OAK APCH'S NORMAL OPERATING PROCS; LED ME DOWN THE PATH TOWARDS THIS POTENTIAL VIOLATION. THE CAPT'S REQUEST TO LEVEL WAS THE CORRECTIVE ACTION. THIS POTENTIAL VIOLATION COULD HAVE BEEN AVOIDED IF I HAD STUCK BY 2 OF MY CARDINAL RULES OF FLYING INFO UNFAMILIAR ARPT: 1) DON'T ACCEPT A VISUAL WHEN UNFAMILIAR; AND 2) BACK UP THE VISUAL BY STAYING ON THE APCH PROFILE (IE; LOC AND GS). ADDITIONALLY I HAVE REVIEWED THE APPLICABLE FARS AND WILL INCLUDE A THOROUGH REVIEW OF CLASS B AIRSPACE PARAMETERS I FUTURE PREFLT PLANNING.