From 99 to 2002 ACRs 99 had the headers, in 2000 they lost the cam and lifters also. I am pretty sure, may be Viper Jeff can find out. I am taking gen 2.
I can tell you whatever you'd like to know about Gen II ACR's. I've had two. The only ACR specific engine difference was the front timing cover assembly. The ACR variant used a specific non by pass oil filter adapter. All other differences are based on model year Viper and carried into all models. As an FYI,
codes...
ACR = Competition Group
CG5P = 5 Point Restraint Driving Belts
SDKP = Competition Suspension
XHPP = Dash Plaque
NNLP = Low Restriction Air Cleaner
WPEP = 18" Aluminum Silver Wheels
LN8P = Delete Fog Lights
AGF = Comfort Group (this added back the Air Conditioning as well as the Radio)
HEAP = Air Conditioning
REAP = Premium Alpine Stereo Radio
These are some, but not all the codes associated with an ACR opton package.