The story of the Porschev is long and complicated, but the seller explains it in detail in his ad here:
This Porsche 912 was manufactured in 1966 where it was bought new a local-well-to-do. The car however was stolen when near new in 1967 and stripped of its engine and a few other parts. The car was purchased, less the engine, by famed endurance racer Dennis Aase. Dennis was a very competitive driver in the 24 Hour of LeMans, IMSA, 24 Hour of Daytona, 12 Hours of Sebring, Can-Am and many other series, as well as being a Toyota factory race car driver. (Bruce Canepa, purveyor of all things important in racing and cars now looks after and actively races Aase's #98 Celica IMSA GTO car.) After Dennis bought the car, he replaced the engine with a 911 motor, added 911S brakes and tranaxle components and took it racing with SCCA. He placed 2nd overall in B-Production that year. After the good season, Dennis was ready for a new ride. Enter Rod Simpson. Rod, a smart, savy car nut and racer, knew of the car and its race history and bought the car from Dennis. Dennis decided he would like to keep his 911 motor though and sold it as a roller. Being a young guy though who didn't quite have the funds to put (at the time) a brand new 911 or 912 motor back in the car, Rod decided that it made much more sense if he engineered a way to put a Chevy V8 in the back. Rod spent the rest of the year designing, fabbing, testing and applying his one off parts to Chevy V8 motor. After less than a year in 1968, the first "Porschev" was tearing up the streets and track. What Rod unintentionally started though was a Porsche hot rodding revolution. While the Porsche purists weeped softly at night, Rod was out running circles around them and starting a massive following. So much of a following, that Rod found he had a business in creating kits for others to follow in his footsteps.
The TL;DR version is that a racer takes a Porsche 912 with a missing engine, turns it into a 911 powered racer, sells the car but pulls and engine to another racer who shoehorns a giant-slaying Chevy small block V8 into the back. It is your standard Disney story of the kid who eats his Wheaties and becomes an Olympic athlete.
Power the Porchev (is it Porsche-Chevy, or Poor-Chevy?) is a "Dart" 400 cubic inch small block that has been ported/polish/cammed/compressed to produce 600 horsepower, but only on a special fuel blend that is 10% tears of Porsche purists by volume.
See a better way to burn some rubber? firstname.lastname@example.org