I'm looking for a h.p. rating for a B.B.C. 1972 454 C.I.CASTING NUMBER 3999289 ALSO A WEB SITE?

Answer 1

Look it up in a Motors manual for the model car or truck it came out of .
What you need is the stamped number on the front of the block .that would referance the year, body, accesory options and horsepower rating. a friendly dealership partsman can look it up.

Answer 2

I looked it up, and I found no horse power reference to that casting number.

3999289 454 72 Corvette 270 HP
3999289 454 72-75 Chevelle
3999289 454 72-76 Passenger
3999289 454 73-79 Truck

Any other information about the block?

If you have the original heads, add the number and I can give you an idea if it is the high performance motor.