You need to use either the blocked or ported insert. You can't leave it out because the material, that the main part of the gasket is made of, won't handle the heat of the exhaust port. However I believe the set I got was flawed. The inserts were thicker and harder than the main part of the gasket. I believe this kept the rest of the gasket from sealing properly causing the gasket to be able to crawl around. I'd measure the thickness of both pieces first. Fel-Pro has lost some quality since being taken over by Federal Mogul.
What happened to the Edelbrock recommendations as per your post I linked in my above post?
"Google Edelbrock:
• GASKETS: Do not use competition style intake gaskets for this street manifold. Due to material deterioration over time, internal leakage of
vacuum, oil, and coolant may occur.
INTAKE MANIFOLD RECOMMENDED GASKET
2121, 3721, 3723, 7121, 7521, 75213 Edelbrock #7220 Port: 1.20” x 2.00”, .060” Thickness
1) Use only recommended intake gaskets set when installing this intake manifold.
2) Fully clean the cylinder head intake flanges and the engine block end seal surfaces.
3) Apply Edelbrock Gasgacinch sealant P/N 9300 to both cylinder head flanges and to the cylinder head side of the gaskets,
allow to air dry, and attach the intake gaskets.
4) Do not use cork or rubber end seals. Use RTV silicone sealer instead. Apply a ¼" high bead across each block end seal
surface, overlapping the intake gasket at the four corners. This method will eliminate end seal slippage.
5) Install the intake manifold and hold-down bolts. Torque all of the manifold bolts in two steps by the sequence shown in
Figure 2 to 18-20 ft/lbs."
I used the 7220. So far no problems. Edelbrock recommended the 1250 set in their 2003 catalog but changed to the 7220 sometime in the recent past. My local speed shop said that Edelbrock changed to the 7220 because of to many problems with the 1250. I don't know whether that included the 1250s or not.