whats the dif in power between the 1981 351 w and the 1970 351w????????

Not a great deal if you're talking 2 barrel engines although the '70 model will still be in front due to compression alone and the fact it has 1.85/1.55 valves and bigger intake ports.
Now a '70 4V engine will be considerably better again with much higher compression and was rated at 290hp gross.
The late 351w engines are way down on compression with big dishes in their pistons combined with a taller deck of 9.503" compared to the '69-'70 engines 9.430" deck. Late engines used basically the same heads as 302's with tiny 1.78/1.45 valves and the little 302 intake ports. Exhaust ports are a much of muchness in all std windsors.

Pete.