what about a 413

That Spirit of 76 looks real nice in the photo.
Have you considered going small block. There is alot you can do with a small block.
You could go with a 430 cu.in. from a 340 block or budget build a 390 from a 318
Using a 4"stroker crank
and a pair of 340 J heads. Maybe deshroud the intake valves.
The 430 would require a 4.125 crank in a 340 block.
It would keep the car somewhat more factoryish and you would have something different. Also it would fit better in that A body. Headers would be easier to install.