Yes they are. The standard Pete Jackson gear drive is not compatible with your knock sensor. What you need to get is the "quite" gear drive for factory roller cams. If you really want one here is what you want:
782-350-91C SB-Chevy with Factory Roller Cam (excluding LT1) $152.99
PJJ-350-91C Small Chevy: 305, 350 with factory roller cam (exc. 1992-up LT1), "quiet " gear drive $152.95
There are plenty of people on these boards running these drives.
'91 Z-28 5.7, SLP 1 3/4 headers, 4 inch Mufflex/Flowmaster cat back, gutted cats, Edelbrock intake, 8.5mm Jacob wires, MSD Blaster coil, S&W subframe setup, Jacob Pro Street Ignition, Harwood glass hood, Spohn lower control arms, complete Kenwood system, and a few hidden goodies.
IDP.........bring'n it back once again!
Forced Induction 427?..........................on HOLD!!!
Stealth Ram......In polishing phase
Soon to be World Castings 427 sbc
SLP 25lb injectors