thanks for all the replies guys. i clicked on the option to be emailed when a response was posted and never got an email, so i just assumed that no one had replied.

Ok, i'll try to answer all of your ??'s

year is 1970, dont know the miles, 650 holley carb
i have tried different brands/weights of oil with no change in knock.
it is an automatic transmission, and does not knock when idling with the car in gear. the sound appears to be louder on the bottom of the engine.

i thought it was a rod, but several people have told me that a rod would continue knocking through high rpms.

the car will overheat at highway speeds. i have done everything i can think of to fix the overheating problem.

i have done the following

-freshly cleaned/rodded 3 row radiator
-new water pump
-new thermostat(ive tried 160 and 180 temps)
-electric fan mounted on front of radiator
-replaced flex fan with a clutch fan
-new radiator hoses
-timed with timing light

what else can i do? would a shroud help?

thanks,
shad