318 Poly in an Early A Body?

You will have to modify the trans tunnel for a 727, not worth it in mho. You are on your own with headers, and a 4 barrel intake is rare and expensive. Then there is the small rear wheel wells. Any LA/ Magnum if done right will make an early Cuda Fly. Even with the stock 273 HP exhaust and manifolds. From 273 to 360. I've had one for 45 years.