First, GM's 650 is flywheel horsepower; not Rear Wheel Horse Power. 650 RWHP is more than 700 or so FWHP.. The reason is drive trains have significant losses.
Of course they are reputable and two of the best. Tell either you want 750-800 RWHP, then ask what drive train changes are needed to handle it. As you mentioned drag racing, you mean high RPM launches, drag radials etc?
Every component of any car including a Corvette has a horsepower rating and the engine can be easily built to exceed that by too much.
I've had racing blood in my veins since I was 16 and I'm past retirement age. Low 10s with a naturally aspirated BBC and low 11s SBC. Today's toy is quicker yet with forced induction..
Although she can make a lot more buy upping the boost-a-pump'voltage and swapping the blower pulley; that would mean running drag radials.. Without drag radials, flooring it would create a smoke screen the US Navy would be proud of.. Winning is the butt squats,the front tires get light, and gone, not sitting, spinning and smoking.