Really,
This could be done, and fairly cheaply.
1. Modern tires and suspension, WAY better...advantage SLC.
2. SLC aero vs 917, I don't know drag coefficients, frontal areas, etc, but the 917 used very simple aerodynamics, so overall....toss up.
3. I don't think you could get the weight down to what a 917 weighed, it was just a minimal number of aluminum tubes and a fiberglass shell, but you could get reasonably close. Besides, aerodynamic drag is going to be your biggest problem at speed. However, advantage 917.
4. On the other hand, weight will be an issue with acceleration/deceleration (both linear and angular). That said, a nice set of carbon-ceramic brakes and a set of modern slicks will give the advantage to the SLC in braking and turning (remember, the 917 was limited to brakes that could fit in 15 inch wheels, and are nowhere near a match for a modern set of binders).
5. As for acceleration...Three factors; power, weight, and the ability to put that power down. Dry sump an LS motor, pressurize it and add some nitro, and you are within spitting range of the 917/30. With the better tires and suspension, and I'd give the nod overall to a well-tricked out SLC. Frankly, with the power that these two cars would be putting down, you'd likely be traction limited in either until (and maybe even in) the top gears.
As with the 917/30, you'd really need someone with the appendages of KING KONG to get the most out of it (assuming no traction control, stability control or antilock braking).
It sure would be fun trying...anyone want to pony up the cash for a monster motor and a Ricardo trans axle?