Did a 409 in a 58 years ago and only problem I recall was the factory cast iron exhaust manifold had to be re-worked a bit to clear the passenger side frame rail. As far as front end weight goes it may be a factor in cars but remember, the engineers designed the truck front ends to work with a full load in the bed which is many more pounds on the front axle than the difference between a BB and SB. With the BB and the bed loaded then weight could become an issue.
