help !!!

i found the casting #s on the block of my pontiac 400 but need help finding out year & horsepower rating can anyone help ?

does anyone have have a way to tell me what kind of 400 pontiac engine is in my firebird engine #s r 318612- Y4 desperatly seeking info !!!

The casting number will cover a number of years and the 400 block was used in an even larger number of vehicles.