ok guys, im looking at buying a 1976 CB750 super sport. the guy has the title it is in by no means mint condition. he also mentioned that there were two different blocks, an aluminum block and a black block. he said the black block was more rare. anyone know if there is truth to this??? the tank has no rust in it. it runs but there are some ignition issues. the locking lid on the gas tank that hides the gas cap is missing. it is lime green with a white pin stripe and has no clear coat left on it. the seat is ripped but everything seems to be there. what would you offer this guy for the bike??? and is there any truth behind the "special black block"???