Test fitting to see where you can run headers is real important on these early A's. I first put a 440 with 906 heads in a stock 65, but had to butcher the shock towers because the head on the passenger side was way too close for headers or manifolds. I relocated the upper shock mount and built fenderwells, and to get tire turn radius i cut into the firewall behind the front tire and made abox for the four tubes. That made a fine foot rest inside the car😁 it doesn't sound like you want to cut the inner fenders, so i bring all this up so you can check now, before investing in something that won't work with the bigblock.