I have a 77 A/C Auto car that I replaced the drive train (and almost everything else) to a 71 ls6 454. The car is a late build 77 and had the R4 compressor and no VIR . GM never built a corvette with a 454 and the R4 compressor. I have an A6 compressor and the corvette 454 mounting brackets. What issues am I looking at if I use the A6 compressor with the existing system. I have the lines, new drier, metering valve etc. I know the A6 is a heavy old unit but you can't kill them and it fits right in the car. Brackets for the R4 to fit the 454 are coming up scarce. It was originaly a r12 system and I have r12. Are there differences in pressures or volume of flow between these compressors? Does anyone have any direct experience with these systems and interchanging parts?