Some where around 240 at about 3800 RPM but that's not what really matters. It's torque that moves large vehicles. HP is just along for the ride.
Torque is about 375 at about 3000 RPM.
Now fuel inject that motor and it really changes.
My 88 Fuel injects 454 Burb was rated 230 HP at 3600 RPM.
The torque however peaked at 385 at 1600 RPM!
Now take that higher peak at a lower RPM with a grain of salt. your engine would still be in excess of 360lbft of torque at 1600 rpm.
What these motors are good at is making BIG torque accross a wide power band. Notice the peak hp was way above where anybody would normaly operate one of these engines for more then a short period when it up shifts. People put too much into Horse power. Semi trucks moving 40k may only be making 300hp but they are poping out over 600lbf of torque.
1959 22' Caravanner
1988 R20 454 Suburban.