GT-40 heads with and intake swap will like to see some 24lb injectors, the 19's will be close to their duty cycle, well explained Hurst and 500HPLX having good vacuum is important with Speed Density and a aggressive cam could cause issues!

 

The speed density computers are tunable, but will require tweeking with every change. The MAF computers are very adaptable and don't require much in the way of maintenance. The MAF swap is not that hard to do, and if you are going to be working with this car for a while, its probably the way to go.

Brian
EFI-Unlimited