Tuna -- Tried this site earlier in the week with the same part number and it has been discontinued. BlackTalon -- You can look for individual pieces on this site (heads, LT4 Hot Cam, etc) but could not find the intake manifold. Maybe I'm looking in the wrong place.
Look back on some of my previous posts a year ago under the same title and you can get a lot of information, most of it from Tuna.
'13 427 60th vert - '21 Silver Flare Coupe - CTS V Wagon(4-door Vette)
Oops. I didn't realize they discontinued this package. Well, they still have it listed but with the "DISCONTINUED" note. And, since they have it listed, they also still have all the parts and part numbers listed with it. I copied them here so anyone interested can put together their own LT1 to LT4 upgrade from their local dealer.
DESCRIPTION: LT1 to LT4 Conversion Kit DISCONTINUED
A bolt on LT4 performance upgrade for your LT1. The LT4 conversion kit includes parts needed to change the top end of the LT1 to LT4 specs. Conversion kit includes:
2 Cylinder Heads P/N 12363287
1 Intake Manifold P/N 12550630
1 GM Performance Parts LT4 Hot Cam P/N 24502586
1 1.6:1 Aluminum Roller Rocker Arm kit P/N 12370839
2 Head Gaskets P/N 12551488
2 Intake Gaskets P/N 12367777
1 Front Timing Cover Gasket P/N 10128293
1 Water Pump Seal P/N 10217886
1 Front Crankshaft Seal P/N 10128316
1 Oil Pan Gasket P/N 10108676
2 Valve Cover Gaskets P/N 10108625
2 Exhaust Gaskets P/N 12552470
Also includes: 1 Distributor Seal(1995-1997 cars) P/N 12552428, and 1 Distributor Seal (1992-1994 cars) P/N 10128317, but only one of these is used depending on apllication.
Not included in the kit, but recommended is the "Extreme Duty LT1/LT4" timing chain kit P/N 12370835.
These are the basic components that make up the LT4 engine and performance please note other parts may be required to properly install these parts on your non-LT4 engine.
1993-1994 ignitions are different than 1995-newer LT1's and may require changing to the newer ingnition system.
Please check with a certified installer before performing this conversion.