I just bought a 1981 bronco and the vin code said it has a 351 windser but it has a 351 modified and from every thing i read they did not use the modified in 1981 also i was told it would be vary e-z to stroke it to a 400 is that possible to do that with out having it bored?

You will have to remove the motor, pull oil pan replace crank and change the push rods and cam but if your are going that far why stop for just that little bit you might as well go and pull he heads have them port and pollished add headers and new high rise intake and bigger carb the remove the oem fan and water pump buy a electric water pump and electric fans to mount on the radatior.