I have a 351w in my Futura. I am running Edlebrock Performer RPM heads, cam, intake RPM AIR GAP, and 800 CFM Carb. All most fits under the hood and would have with the right Air Cleaner. Just needs to be about 3/4" - 1 " lower to clear nicely. The Performer intake would help a lot as well.....The Air Gap intake is quite a bit taller.
I also am using BBK Shorties for headers....fit great with no issues.
You will need to make sure you have v8 coil springs too, beefier radiator, and different throttle cable ( shorter for v8's).