the late 70's -81 preheated duct was a black colored fine aluminum corrugated piece, unlike the '68 - mid 70's black colored Pontiac preheated duct which had a fine wire and inner cardboard construction. Many local autoparts stores carry an alum preheated duct that is similar to the late 70's style, but not exact. The plastic elbow that attaches to the 79 400 and 301 aircleaner snorkel is a special mitered style, only used by Pontiac, in order to clear the stock valve cover with the stock 1.5" deep drop aircleaner base. I try and stock em nice used, but usually need them when shipping out Formula and T/A aircleaner assembly's.
The clamp that attaches the mitered elbow duct to the aircleaner snorkel is a standard tower clamp like originally used on a radiator hose. These were used through the late 60's and up into late models...a junkyard piece, unless you want to buy a repro from Ames or Motor City Muscle (Inline Tube- Kryta's). On the late '70's T/A's, originally there was no crimp clamp used at the ex manifold shroud. On late 60's Pontiac V8's up through at least the 72 455 HO engines, the corrugated wire/cardboard style preheated tube used a thin crimp style clamp to attach the duct at the ex shroud, then the top end just slid onto the elbow. For many years sourced the exact style crimp clamp at local Maytag washer/ dryer sales and repair shop. Another detail piece now avail from Pontiac catalogue vendors. Hope this helps.