Looking for 11's
I would vote for the 451. It will provide the best fit in an a body,as it uses the 400 block. Pistons are extremely light,making for a very quick revving engine and it has the 440 stroke and rod ratio if using 440 rods. Makes for gobs of torque.500 horse is easy and 600 not hard at all even with stock heads. It also has to be one of the most budget friendly big block combo's of any make,as it uses stock components and off the shelf pistons.
Slap a solid cam in it,cal tracs out back and a good solid frame to elimintate as much flex as possible. Loww 11's are easily within reach,and 10's are very possible with tuning.
The only issue with it is headers. There are some available,but either fenderwell,semi fenderwell or min ground clearance. The shumacher is probably best fit for the street,but its got small tubes.