The RR/GTX/RT/SB motors were supposed to get chrome caps according to factory literature, but some came through with black. Non-performance motors were supposed to get the standard black caps. The dual-snorkel air cleaner would be Noise Reduction Package performance motors from what I can tell on original cars (with the 330-horse 383s and 350-horse 440s apparently getting them too). The small unsilenced air cleaner was the "performance" unit otherwise. My '69 RR A/C car had the dual snorkel type but my non-A/C RRs had the small one; these were original unmolested cars. All my RRs & R/Ts had chrome oil caps, even that A/C car, which had the 330 motor. My '70 383 4bbl Satellite had a black cap.
I'm sure there were occasional exceptions to the air cleaner & filler cap "rules".