There's nothing easy about swapping anything into the cozy confines of the early A's engine bay! The factory single exhaust and manifolds are pitifully inept for anything high HP, headers are pricey, the inner fenders are right there in your face, the brakes and front suspension are marginal, and with a big block in there, all that will have to be beefed up! There are guys who have done this swap, but it means changing everything underneath, none of it will hold up to the extra weight and HP of the big block stuff! You need heavy duty stuff to do it right!! This is your son we are talking about here, very precious cargo, it needs to be safe!!!
I bought a 71 Dart from 2 good old boys up north in my state! It had a 440 built by Muscle motors under the hood where a slant 6 used to be!! You guessed it...9" drum brakes, slant 6 torsion bars and spindly suspension, and a 7 1/4" rear! It also had a full length dent down the passenger side from its only trip down the road, where they wound it up and put it into a ditch!! That motor is still in my buddies race car running 10's!! Moral of the story??....you gotta have the whole bull, not just the heart!!!