tapping noise in motor

thanks for the info 534 bc. the noise seems to get a little louder after the motor warms up. but not unbearable. also the blazer is a 97. i also purchased a bottle of lucas oil additive, dumped that in might of quieted it down some but cant really tell with my hearing. one more question if i get a used motor from salvage yard, will a newer 4.3 work or do i have to stay with 97 yr. thanks again. buff691