I think the SBS is an apt update to Bond's role and capacity in WWII in naval intelligence, though the SBS was formed then, just as the SAS was (which in turn was subsequently desolved and then reactivated). The SBS in WWII were actually very similar to the commando activities carried out by Fleming's 30 Assault Unit, particularly by the covert MO of their missions, vs. the more prominent raiding done by the Army and Marine Commando. I think giving Bond an SAS background would have been cheap and exploitive storytelling and I like how Bond has been portrayed as different and at times in competion w/the SAS.
"...the purposeful slant of his striding figure looked dangerous, as if he was making quickly for something bad that was happening further down the street." -SMERSH on 007 dossier photo, Ch. 6 FRWL.....