I'd go with using the inner headlamp holes for ducting too. I don't know what CFM your carb is but I can tell you it's a double pumper, it's way too much for a standard Rover engine regardless of its CFM. If it does turn out to be a 390 double pump, sell it as they're a rare bit of kit.
If it were me, I'd be seriously thinking about fitting a Weber 38DGAS carb from an Essex V6, much better economy than a Holley which even as a 390 is a bit big for a stock engine, it'd be a piece of doddle to adapt to your SU manifold too.
I think you're going to have your work cut out doing anything with that front suspension.