Looking to upgrade your engine with some high-quality Oval Port Heads? Check out these 1971 Big Block Chevy BBC 402 454 Heads with part numbers 3993820 and 820. These heads were manufactured by GM and are compatible with OE/OEM part number 820 and manufacturer part number 3993820. Dated L-15-70 and L-28-70. Cleaned  and checked  for  cracks. No porting or polishing.  Nice pair to do up. #145