Simon,
I am running a 4.3 Rover built some years ago by JE Engineering in Coventry.
At the time it was dyno'd at 280 hp at 6000RPM with 299 ft-lbs of torque. What was more impressive was 200 ft-lbs at 1500 rpm. As Russ said above, there is gobs of torque. I used 4 downdraught double choke Dellortos (cheaper than Webbers but look and sound the part).
The best bit as mentioned above is the weight. The all ally block and heads means that the complete engine with flywheel, clutch and induction comes in just over 330 lbs. Combined with a steel monocoque chassis the curb weight of my GT40 is 2210 lbs as measured on a public weigh-bridge.
I would gladly trade 70 hp for 150 lbs in weight in this sportscar (compared to a 302), since the lighter weight helps everything; acceleration, handling, cornering, braking, chassis stiffness, gearbox reliability.
Trevor