You do not use the factory shrouds with aftermarket elec. fans, they come with their own shrouds and mounting points. The factory elec. fan shroud combo was available on 1979 and later L82 Corvettes, the elec fan was controled by a temp switch on the right cly. head which would turn the fan on when high temperatures were incountered. This single elec. fan is not designed or capable of cooling the car, it simply helps the mech. fan when needed. Aftermarket elec. fans can work, if they are installed correctly and you buy a quality set. A good set of dual elec fans capable of cooling a corvette will cost about $300, they should pull at least 2500cfm. A single elec. fan that pulls less CFM will not keep you car cool. There are alot of cheap fans out there that pull 1500 cfm or less.  I have a SPAL dual elec fan unit that pulls 2750 CFM they also require about 35 AMPs so I had to install a 140 Amp alt. to handle the load and run a 2 Gauge wire to handle the higher current. It is an expensive mod. $500+ but keeps a 400hp Corvette cool even during the hottest days. Hope all this helps.