both engines if properly tuned, on a mild build, should provide about 1 hp and 1 foot lb of torque PER CUBIC INCH OF DISPLACEMENT
while its true the big block probably will weight about 120 lbs more the difference in power far overcomes the difference in weight
play with this calculator and assume the sbc chevelle weights 120 lbs less than the big block version, but weights a realistic 3700 lbs, and makes 350 fly wheel hp vs the heavier cars 454 flywheel hp and 3820 lbs
now assume both cars loose 20% in drive train losses
Your ET / MPH computed from your vehicle weight of 3700 pounds and HP of 280 is 13.77 seconds and MPH of 97.29 MPH.
Your ET / MPH computed from your vehicle weight of 3820 pounds and HP of 363 is 12.76 seconds and MPH of 104.96 MPH.
the calculations may not reflect reality exactly but , they do show the realistic fact that the larger displacement should produce a slightly faster car.
now obviously your going to have someone point out that the big block tends to cost a bit more to build, but its also a good deal harder to make the same power with the lower displacement, given your low budget of only about $700 to -lets say $1000 or so,or so, a good used performance intake, decent flat tappet cam, maybe headers are about all your going to do to either engine