Running a '65-71 intake on '72 & later heads with a functioning heat crossover w/o the passenger side '72+ intake gasket burning out is a relatively easy fix. I've referred to this fix several times, it flat out works. the stainless steel shim blockoff piece can be made in 15 minutes. Stumbled onto this solution many years ago dealing with a local who desired running his '65 GTO's tripower set-up on an .030 400 with 6X-4 heads. Just running the '72 intake gasket, it burned out right below the "dead spot" of the heat crossover, thus the need to block off to the bottom of the divider under the "dead spot" on the later style head. Since that first installation, have used the same stainless steel shim trick on over a half dozen other Pontiacs. No need for expensive intake swaps or just blowing off being able to run a '65 or '66 tripower intake on an engine built with '72 & later heads.
Making the stainless blockoff shim. First one needs a thin piece of stainless steel, not thin steel, or aluminum. The stainless steel needs to be thin, thin like the stainless shim gasket piece used on '67 Q-jet intakes. Years ago, I eventually struggled coming up with a readily avail piece of scrap thin stainless steel. Over the last two decades, many vehicles use a thin stainless steel piece that inserts between the brake pad & the brake caliper pucks. My sons 4Runner is one of many vehicles tht uses this piece of stainless, behind each brake pad. Its a piece of stainless steel that gets chunked everyday in shops across the country when a new pair of brake pads & stainless shim pieces are installed.
With a castoff piece of stainless shim from a brake pad replacement, along with a Dremel tool with 1" diam cutoff wheel, it is a simple matter of laying out the pattern & carefully cutting out the following shape.
Visualize the needed block off shim as the top of a capitalized T logo similar to what used on a University of Tennessee logo.
The top of this T is 4 5/8" wide.
The outside edges drop down 1 1/2"
Then on each outside edge, one kicks inwards 3/8".
Next, one goes straight up 1/2".
Next, one will have have to cut across (parallel to the top edge) 3 7/8" to connect the bottom plane.
Once the stainless shim is cut out, it is inserted on the passenger side. Between the heat crossover area on a '72 & later Pontiac cylinder head & the to be lined up '72 & later style intake gasket. The two 3/8" wide "legs" need to be carefully slid down abutting the top edges of the two center intake bolts. If one one likes, one can get creative with the Dremel tool & cup the shape of the two 3/8" wide legs so the legs are located to a small degree by the two center intake bolts.