if you've every heard a rob knock, then you would know if it is a rod knock or not... its a very distictive sound , especially with these engines...
my buddy's 240 has a bit of a knocking type sound, on the number 2 piston... its the valve seal on what seems to be the front exhaust valve...
you've really got to narrow down where the noise is coming from...
if its down low on the block, then its probably rod knock, it it is in the head, then its got to do with the valves... if it seems to be both, one then the other and back and forth,then it is probably a bad wrist pin...
good luck