The big issue with these manifolds is the flat or depressed areas at the front and back corners(left to right).If you pump fuel from the accelerator pumps before starting or have a float or needle valve issue the raw fuel puddles in these areas and the slightest kick back or backfire ignites the fuel and fumes causing a hard explosion.If you look in the manifold you will see the blackened area where the fuel/fumes ignited.
Indy has an insert(epoxy) that helps but fuel can get behind and under it,it also kills the volume of the intake which makes this intake work so well on large cubic inch engines.We maximize the volume buy welding in small angled ramps at these areas.We also install the Wilson or similar valves for extra insurance.