I know a well funded west coast Ford SB heads up 10.5 outlaw racer that went faster with a Dart cast iron filled block than they did with a filled Fontana aluminum block on NOS and with both super chargers and turbos
The rings sealed up way better and held the vacuum a lot better with the iron block than it did with the aluminum block towing it every where except for the burn out and the run
They where able to keep the weight the same as well as the weight on the front and back tires
Test, test and test some more, if you want to go faster than every one else in your class