Aluminum /6

An aluminum block slant is a poor choice for a drag engine, They suffer from cylinder walking with high compression. The tops of the cylinders aren't connected to anything. Everything I have read from /6 racers says to stick to an iron block for a serious racing engine.
It is unlikely that a 63 Dart would have an aluminum engine unless it was swapped in by a previous owner. They were fairly common in 60 and 61, by 62 almost none were put into cars. Owners didn't change coolant frequently enough and they suffered from internal corrosion problems. That's why they were phased out in just a few years.