Yes, I built that engine. Owner is in Wichita, KS, with a '69 Mustang. With the right ring pack, a vac pump will add a whole lot of horsepower....definitely worthwhile with the correct bottom end parts. This engine used ultra low tension rings and the pump pulled about 10 inches of vacuum. My educated guess is that it added about 30-35 hp.
If your bro's heads haven't been ported, I would expect about 625 hp. He doesn't have enough camshaft....needs about 10 degrees more duration.
The engine above was 13.5:1, with a 263/275 @ .050" stick, .850" lift on both sides, with a T&D 1.8:1 race rocker setup. It peaked at 7000 rpm. Heads flowed 380 cfm with a 2.250/1.65 valve setup. 4.155" bore size with a 4" Callies crankshaft. Quick Fuel 1000 cfm Dominator, with a 4150 CHI intake, port matched to a Super Sucker 2" adapter spacer.